Category: Marine Plant Guide

The term “marine plants” is often used loosely in the aquarium trade to describe both macro algae and sea grass. Macro algae, unlike sea grass are not true plants but are actually large celled algae. They absorb nutrients through their cell structure instead of the root system as terrestrial plants do. All macro algae are photosynthetic and thus rely on the sun’s energy for food. Marine plants serve as the base of our ocean’s food chain, providing food, oxygen and habitat for thousands of marine inhabitants. Unlike marine plants (sea grass), macro algae lack conductive tissue, true roots, stems and flowers. Instead of roots they have holdfasts or rhizomes in which individual runners support the growth between blades or stalks depending on the species.

Marine plants grown in the aquarium will thrive under the right conditions and offer a replenishing food source to tank inhabitants.  In addition to converting sunlight to energy they also require nutrients to grow. It is generally accepted that all marine plants require the same essential nutrients as aquatic and terrestrial plants do. The major nutrients required by marine plants are nitrogen, phosphorus, potassium, sulfur, calcium & magnesium. The minor nutrients are iron, manganese, copper, zinc & molybdenum.       

Marine plants are distributed worldwide and are found in some form in almost every ocean on the Earth. There are two distinct habitats where macro algae are found, temperate or cold water algae, and tropical varieties. The tropical and sub tropical species are of most interest to hobbyists to culture, as the cold water species have special needs requiring a climate controlled environment (chiller). Throughout the world, marine algae grow at varying depths and environments so some are more suitable for culture in the aquarium than others. Several species can even be successfully kept with lower light as they are found and collected from deep water habitats, while others need a brightly illuminated habitat to thrive.

There has been much debate among marine aquarists over which individual species are best suited for culture in a refugium or display tank and which should be avoided all together. Some species are fast growing, invasive and can be a nuisance in any aquarium, especially reef tanks. Despite their often invasive qualities, they’re many beautiful species of macro algae that are unlikely to be introduced to non native regions but are easy to grow in a marine aquarium. For the aquarist interested in the culture of macro algae there are hundreds to choose from, but only a few tropical species that are really suitable for aquarium use. It is these species that will be covered in detail.

The three main classifications of marine macro algae are Chlorophyta (green algae), Phaeophyta (brown algae), and Rhodophyta (red algae). They derive their names from the dominant pigments associated with each species. All of these classes also contain slightly calcified or heavily calcified algae, which depend upon properly maintained calcium levels to grow and reproduce. Sea grasses have their own classification (Magnoliophytae or Angiospermae) and will be covered separately. Mangrove plants are also discussed, as they are often used by hobbyists in the marine aquarium. Although their growth is slow and overall nutrient uptake limited, they remain popular additions, especially in a refugium.

Beginning in the early 1980’s a strain of Caulerpa known as taxifolia was used as a tank decoration in several marine aquariums in Germany and was then successfully propagated and distributed for use in commercial aquariums across the globe. This extremely hardy and more temperature tolerant strain was soon discovered to have escaped into the waters of the Mediterranean and was found growing in large patches near shore. This highly invasive species has since been discovered worldwide, most notably off the coast of California, USA and New South Wales, Australia. The introduction of the hybrid Taxifolia is blamed on the ornamental aquarium industry, reportedly being released only feet from the famous Monaco Aquarium where it was being used as tank decorations. Because of its invasive qualities and toxicity to herbivorous fish, Caulerpa taxifolia and a few others are now banned for sale or distribution in several U.S. states as well as many countries. Needless to say, this particular type of macro algae should be avoided and its popularity and availability has decreased in the United States considerably in the last decade.  

Russ Kronenwetter is the owner of Gulf Coast Ecosystems, a wholesale and retail supplier of collected and aqua cultured ornamental marine algae. He is an avid scuba diver and experienced marine life collector, with over 25 years experience in the marine aquarium industry.

My interest with keeping tropical fish began at an early age growing up near the Florida Everglades in South Florida. With a bucket and net in hand, I would often spend entire afternoons with my brother, wading through alligator and snake infested waters in search of freshwater tropical fish for our small aquarium at home. As I grew older, my attention gravitated to the marine aquarium hobby. The fish were more colorful than freshwater varieties and the amount of invertebrates available were interesting and fascinating to me.

I began exploring the shallow coastal tidal pools and protected shorelines of the Atlantic Ocean , collecting marine tropical fish for our home aquarium. About the time when reef aquariums and live rock began to gain in popularity, I was now living on the Gulf Coast of Florida. The fish weren’t as colorful; the water not as clear, but something else was abundant. Marine macro algae were growing everywhere!  The warm tropical waters of the Gulf of Mexico in Florida are full of a wide array of fascinating and colorful marine algae. Like many other hobbyists in the early 80’s, most of my interest was with growing various species of hardy Caulerpa. I soon however, began experimenting with growing other more colorful and challenging varieties including both brown and red algae.

My first attempts at culturing marine macro algae were marked with some frustration and failure, but I continued learning and experimenting until I was able to successfully maintain several species in the home aquarium. I was once told by a reputable pet store owner that macro algae couldn’t be grown. He had tried it and was unable to keep it alive for any great period of time. This was years before the “refugium” made its appearance, so keeping marine algae in captivity long term was a relatively new idea and its needs largely unknown. Most of the information contained in this publication is related to both my personal experience and observation. I was originally hesitant to publish the book, as there are others that are much more qualified to do so, but still to date, there remain very few resources for the marine hobbyist.

Let me first say that I am not a biologist, but an avid aquarist with many years of experience maintaining saltwater aquariums. Most literature available on marine plants today is technical and often requires advanced knowledge to understand. In addition, the majority of books on the subject are mostly field guides for students and lack detailed information on aquarium use. The purpose of this publication is to offer a simplified guide for the identification, use and culture of marine macro algae and plants in the aquarium.

Marine macro algae and sea grasses have had a long history of importance throughout the world, with their use dating back to ancient times. Today, many varieties have important economic and commercial value. Marine algae is used in thousands of products including fertilizer, bio-fuel, ice cream and even cosmetics. In several cultures it is highly prized as a food item and is a major part of some island diets. Its appearance in the aquarium industry began sometime in the late 1970’s, with several species of Caulerpa used mainly as tank decorations.  

With the many innovations over the past several decades in marine reef keeping, marine plants have increased in popularity among saltwater aquarists and large scale commercial aquariums. Today, many in the aquarium industry favor a more natural approach to marine aquarium keeping. Marine plants not only improve the health of fish and corals in captive systems, but are nature’s nutrient consumers, effectively removing nitrates and phosphates to nearly undetectable levels. Another benefit is the food value of many species of macro algae. In their natural environment, fish and invertebrates feed continuously during the day, consuming large amounts of micro and macro algae.

A fairly new trend in the marine aquarium hobby is creating macro algae and sea grass dominated aquariums. These systems are quickly gaining popularity as a change from the normal “reef” setup. They are very popular with marine aquarists that are interested in keeping peaceful fish and invertebrates, such as seahorses, pipefish and dragonets. Just like a freshwater planted aquarium, there’s something alluring and fascinating about the sheltered lagoon habitat where marine plants play host to juvenile fish and invertebrates. The world’s oceans are filled with a fascinating array of marine plants, some so striking and beautiful they often look like creatures from another world. As the marine aquarium hobby progresses, many more of these species should become available for the aquarist to observe and enjoy in the home aquarium.

Finding a reliable source for the purchase of marine plants can be challenging at times. Most varieties are only offered seasonally as they are collected from the wild. The good news is that today the amount of online retailers, as well as pet stores that provide macro algae and sea grass for sale, are increasing annually due to high demand for new and interesting specimens. Some slow-growing and rare species can be very difficult to obtain and are best acquired through a fellow hobbyist or local aquarium club. Just like corals, most cultured macro algae is hardier and more tolerant of aquarium conditions as it has been acclimated to survive under less than optimal conditions. The major cultured varieties are Chaetomorpa, Gracilaria, Ulva and some species of Caulerpa. The best place to purchase marine plants is from your local pet store or hobbyist as these specimens can be examined for health and possible undesirable hitchhikers. As the popularity of the refugium and planted aquariums increases, many pet store owners are realizing the benefits and profitability of carrying different varieties of colorful macro algae for their customers

If you’re unable to locate healthy specimens, most macro algae are very resilient and can be nurtured back to health within a few weeks if given the proper environment. Sea grass specimens however, must be in optimal health with fully intact root systems to survive. Look for specimens that have new growth at the tips or roots and appear healthy and green. Most varieties of red algae will not tolerate any drying of their fronds and should always be submerged or transported completely wet. Healthy specimens of Caulerpa will have new growth at the tips and will not have numerous clear and yellow fronds which is an indication of poor health.

When purchasing specimens online, be sure to inquire how the plants will be shipped, as packaging and carrier methods vary greatly between different vendors. Most macro algae, sea grass and mangroves ship fairly well and can be shipped for durations of 24 hours or more with good success. The important thing to consider when purchasing product online or through a catalog is the quality of the specimen when collected and the facility in which it was stored prior to shipping. Too many times wholesale distributors and pet stores don’t give attention to the needs of the plants and they are stored in terrible conditions with little or no lighting, inadequate water flow and improper filtration. Choose vendors that have a solid reputation and readily share information on acclimation and care.

A thorough inspection of the plants prior to introducing them into an aquarium or refugium is necessary. Pruning of dead or discolored tissue and removing any undesirable hitchhikers will greatly aid in the acclimation of new specimens. It is also recommended that macro algae and sea grass specimens be quarantined, especially if adding to a system with seahorses, pipefish, etc, that are more susceptible to disease and infection. Depending on the species, it is beneficial to drip-acclimate macro algae to its new environment as any sudden change in water quality can often induce a sexual event causing the plant to sporulate and die. Caulerpa species will not tolerate sudden changes in water temp, ph or specific gravity and have built in indicators to send out reproductive spores when conditions change suddenly.

Identification can sometimes be difficult between different species of macro algae as many are very similar in composition. Just like with marine tropical fish, many species are sold incorrectly or mislabeled at the pet store. While this is not normally a major issue, it helps to properly identify the species in order to care for it. Keep in mind that some deeper water species will not tolerate poor water quality, such as the beautiful Botyocladia and many of the algae from the Pacific. When introducing macro algae and especially sea grass specimens to a new aquarium, it is generally a good idea not to overstock as they need time to adjust and get established. One exception would be a sea grass dominated system. Most sea grass grows very slowly; in fact, Turtle Grass can take a year or more in the wild to re-colonize an area after its roots have been disturbed. For this reason, it is a good idea to provide fast growing specimens, such as Caulerpa, to help in the maturing of the aquarium so that nuisance algae does not take over, while root systems are developing. Even in the most well equipped aquariums, some species will do better than others and some unfortunately will simply refuse to grow. With this in mind, it is worthwhile choosing a variety of species to see which do better in their new environment.

The popularity of marine plants in the aquarium is no more evident today than in the addition of a “refugium”. The use of a refugium is a natural, beneficial way to balance and promote a healthier marine aquarium. A refugium can be defined as any separate system that is connected to another tank for the purpose of creating a protected environment for beneficial marine flora and fauna to grow without predation by fish and invertebrates. A refugium typically contains small amounts of live rock, various macro algae, and a deep sand or mud bed. These systems can not only improve the water quality of marine aquariums by removing nitrates, phosphates, carbon dioxide and some metals, but in time can provide a live food source for many marine species by hosting different larvae and invertebrates.

They’re numerous commercially manufactured refugiums available today, in a wide array of styles and sizes to suit almost any desire or need. Many of these add-on systems are getting larger and more advanced so that hobbyists with large aquariums can enjoy the benefits of a refugium with reduced maintenance and care. The most popular style of refugium is one that is placed directly under the main tank as part of a continuously flowing system that allows the tank water to move through the sump and then back into the main system via a return pump. This style often includes a pre-filter sock or other media that traps large debris before entering a separate lighted chamber where marine macro algae and/or plants are grown. Most models also have separate chambers for a return pump and/or a protein skimmer. For those wanting a larger surface area or a more custom design, a simple system can be made out of almost any container or aquarium sturdy enough to hold sand, rock, water, etc. Dividers can be made of cut sheets of glass, acrylic or screens to separate the mechanical and biological components.

For aquariums that lack the space below the main display, there are several options. First, a separate tank can be placed beside, behind or above the main display tank and plumbed with an overflow box and/or bulkheads. This style can present some challenges, but allows for the most visibility and enjoyment of the refugium. Another option is a small hang-on-the-back refugium. These smaller versions can be added to systems that lack the appropriate space to include under the main display tank or for aquarists that don’t want it in direct view. These most often include a small circulation pump that draws aquarium water from one end of an acrylic box and out the other end. Although small in size, they can be effective in smaller aquariums up to 30 gallons. 

Flow rates can vary greatly in these systems, but most favor a high turnover ratio, as much as 10x the water volume per hour. Larger display tanks featuring corals and invertebrates can benefit from even higher flow rates. In their natural environment, most marine flora and fauna live in a dynamic place, with strong currents and constantly changing tidal surge, so they are quite accustomed to adapt to varied levels of water movement.

Some commercially available refugiums include a light, usually a 9w to 18w compact fluorescent or led fixture designed to fit just above the sump. While the amount of light may be fine for some macro algae, it’s often more desirable if space is available, to upgrade to a higher output light source, such as led floods or t-5 fluorescents. Overall, it depends on the size of the refugium and what the purpose of it will be. For most, the concept of a refugium is to export nutrients quickly and efficiently, so why deprive the algae of what it needs to thrive with a low light environment? On the other hand, if the purpose of the refugium is to provide an area for the reproduction of invertebrates to feed the main tank then strong lighting to provide optimal growth is not necessary.

Proper maintenance of marine planted aquariums is a necessary chore for long term success. Like most aquaria, if the habitat is neglected the inhabitants will likely suffer and various micro algae will soon invade, turning a beautiful aquascape into a container of pea soup. Unlike coral dominated reef aquaria, marine plants produce large amounts of organic material, which in turn can form large deposits of nutrient rich substrate or detritus. While some amount of organic material can be beneficial in storing nutrients and even necessary in sea grass aquaria, the accumulation will almost certainly feed unwanted growth of nuisance micro algae. As mentioned previously, water changes are the single most important measure to maintain a healthy, balanced ecosystem. Depending on the size of the aquarium, a weekly water change of about 25% is enough to continually maintain a planted aquarium. In large systems with high evaporation rates, biweekly water changes are normally just as effective.

Cleaning sediment and organic material from the aquarium substrate is a controversial subject for some aquarists. It can be done by natural means or by manual removal. It is not recommended to disturb the sand bed too much, as the sediment released can cover the plants, rocks and other inhabitants. There are many beneficial invertebrates that can be added to a marine planted aquarium to aid in the cleaning and removal of organic material. An important aspect is to not overstock, as the “clean-up crew” will become counterproductive, often preying on each other. Various worms, copepods, amphipods, sea cucumbers, reef safe hermit crabs and snails will provide a natural way of keeping the substrate aerated, healthy and clean.

Many aquarists employ a small pump to create “miniature storms” within the tank so that the mechanical filter can extract most of the floating particles and also provide food for some invertebrates. This can be helpful in some aquariums, but densely planted aquariums often will suffer as the sediment completely covers the plants. Gently vacuuming the top layer of a the substrate is popular with freshwater planted aquarists, and can be done with care in marine planted tanks. This does not work very well with fine sand substrates however, and can remove beneficial fauna from the tank.

Besides maintaining the overall water quality, most of the maintenance in a planted aquarium is concentrated on the plants themselves. In a healthy environment, most marine plants will grow at a very fast rate. If left unattended, they will reach a critical biomass and slowly die or outcompete another species for available light and nutrients.

Caulerpa species are among the fastest growing macro algae and will need regular pruning and control. Fish may be employed to do the task, but will often devour entire colonies in a short time. Simply removing plant material is the best method of control. With Caulerpa, simply divide the colony into even parts by pinching the rhizome between your fingers or by using surgical style scissors. Most species will form a ball of mucus at the rhizome and/or secrete a small amount of organic chemical, but this will heal quickly. Red macro algae grow much slower than green, but several species such as Botryocladia and Halymenia can overgrow an aquarium. Red algae can be cut or torn at any location without harming the plant. If a holdfast is present, growth should be removed from the top portion, as this attachment takes time to develop. Regular trimming of clear or old growth is recommended as some larger species will reach a critical biomass as nutrients are exhausted in the aquarium. Some species will release a chemical when cut, but the effect on other species is minimal. For the most part, brown macro algae are very slow growing and need very little maintenance. Sargassum can grow quite large and may need to be trimmed occasionally to allow light to reach the bottom of the aquarium and other species.

All marine plants are photosynthetic organisms and require a specific spectrum of sunlight to survive. Without the proper lighting, photosynthesis will be impaired and the algae and or plants will slowly die. The conditions that marine algae are subjected to in captivity are very different from those found in their natural environment. A typical aquarium is both nutrient and light deficient so marine plants must adapt to live under these artificial conditions. Without question, the use of some form of natural sunlight is the best way to grow marine algae and plants in an aquarium, but for most aquarists this is not an easy arrangement. Thankfully there are many capable artificial lighting systems that can achieve a similar spectrum necessary for photosynthesis. Most basic aquariums today feature a single full spectrum fluorescent bulb, but although it will illuminate the tank inhabitants, it is grossly insufficient to grow much of anything unless the tank is very shallow. Providing the proper lighting is an area that many hobbyists fail with respect to growing marine plants. Instead of providing a lesson on how plants and algae convert light to energy, we will focus on the proper spectrum and intensity needed for successfully growing marine plants in the aquarium.

Light spectrum ratings are identified by the Kelvin temperature scale.  The lower end of the Kelvin temperature range bulbs are most suitable for growing marine plants and are typically available in the 5000K – 6500K range. If your aquarium will include soft corals, most marine plants will also grow quite well under 10,000K lighting. This is normally a more pleasing spectrum to the eye, as the lower temperature bulbs can appear green or yellow. Unlike terrestrial plants which grow above the water or submerged at shallow depths, macro algae grow in different spectrums of light depending on the depth and species. Depending on the intensity and kelvin temperature the changes in color among different species can be quite dramatic. There are a few varieties of red macro algae for instance, that can be found in shades of red, yellow and brown within the same species. The distinct coloration is caused by the pigments associated which each species and the spectrum of available light it receives. Overall most macro algae and sea grass will do well under full spectrum lighting. The exception is with some varieties of red macro algae, which prefer a much bluer spectrum and can benefit from some supplemental actinic spectrums. Mixing color temperatures is preferred and is the most appealing while still allowing for optimum growth. Too much red spectrum can fuel the growth of less desirable algae both on the macroalgae and in the substrate.

The same principles that apply to freshwater planted systems and some soft coral dominated aquariums translate to the marine planted aquarium and/or refugium. As a general rule, most marine plants and algae need roughly 3-4 watts per gallon of full spectrum lighting to grow. Of course, this is an older style formula that has certain limitations and must be adjusted to allow for very small aquariums or those that are deep. Also, if using a high output fixture (vho, metal halide, led floods), less watts per gallon are generally needed and the par value is much more accurate when determining how much intensity is actually needed to penetrate the water column. A few deep water species can do well in low light conditions, but will grow much slower in this environment. Sea grass however, need large amounts of intense full spectrum light.

The most common types of fixtures available to light a refugium or marine planted aquarium include fluorescent, metal halide and led fixtures. The brightest but least energy efficient are the metal halide fixtures and the least bright and or efficient include standard output florescent fixtures.

Fluorescent Tubes

Fluorescent lighting is an older, less efficient way to light an aquarium and most modern manufactured aquarium lights are now powered with leds. High output florescent fixtures are still popular with some hobbyists because of their excellent kelvin and par ratings, but have a higher operational cost due to the short lifespan of the bulbs and the amount of energy required to power the ballasts. The high output bulbs include very high output (VHO) and high output (T-5 HO). VHO lighting is an excellent fixture for growing marine plants, but has been replaced by the popularity of a newer technology, the T-5 high output fixture. Similar in intensity to the power compacts, the advantage of the T-5 is that the amount of light is spread more evenly over the aquarium. They are also more economical and take up far less space than traditional T-12 and T-8 bulbs. In general high output florescent fixtures are completely adequate to grow almost any species of marine macroalgae.

LED (light emitting diodes)

Led light fixtures have come a long way since their introduction into the aquarium hobby more than two decades ago. They’re the most efficient fixtures, using about 70% less energy than a typical metal halide fixture. Because they are not actually bulbs, they require a lot less power to run as well as much less heat. The fixtures can be mounted closer to the surface of the water so they also are better at penetrating deep tanks. In addition to being very energy efficient many fixtures have fully programable spectrums and intensities. The flood style led fixtures offer the most intensity and highest par values for lighting a marine planted aquarium. The most efficient light fixtures have a high CRI (color rendition index) or PAR (photosynthetic active radiation) value and offer the hobbyist the most beneficial light available to marine plants. Again the best kelvin temps are in the 5K to 6500K range. Although they’re a modern and economical choice for aquarium lighting, leds don’t last forever and eventually the phosphorus coating will start to disintegrate changing the color spectrum altogether. Although sufficient for many species of macroalgae, some species don’t grow as well under available led spectrums.

Metal Halide

Metal halide lighting is the best lighting method for the reef aquarium to date. Even with all of the innovative technology in modern led lighting it’s unlikely they will ever replicate the spectrum quality and intensity of metal halide bulbs. The problem with metal halides is that they require an excessive amount of wattage to power even a small 100w fixture and produce a lot of heat when operated. The bulbs must be replaced every 6mos to a year as they lose their effectiveness over time. For this reason, they have largely been replaced with more energy efficient fixtures such as leds. Some hobbyists still use them despite the drawbacks, so if you can stomach the high operational costs it’s an excellent choice for a marine planted aquarium.

In the marine aquarium there are three main types of filtration that are essential to a clean and stable environment. They are mechanical, biological and chemical. There are many commercially available products that combine these in one unit, such as canister filters, power filters and trickle filters but most are not suitable for a marine planted aquarium. Many of these designs will become nutrient sinks in time and can release large amounts of nitrates and phosphates into the aquarium water. While flow-through filters may be beneficial for some heavily planted aquariums and even necessary, generally it will create conditions favorable for excessive, undesired micro algae growth without regular cleaning of filter material. Maintaining an aquarium with marine macro algae and plants is often a balancing act between controlling the buildup of nitrates and organic material and providing just enough for a healthy ecosystem.

Mechanical Filtration

For the marine planted aquarium the use of some form of mechanical filtration is normally needed. Plant material in time will break down to form sediments that can become nutrient sinks over time, especially in smaller aquariums. Some of this organic material will break down and be consumed by both macro algae and sea grasses but will also encourage micro algae growth. Depending on the size of the system these include the use of foam filter pads, micron filters and sock filters. Filter material should be cleaned or replaced often as they get dirty quickly in marine plant dominated systems. Protein Skimmers are very efficient at removing organic material and can be used in large systems that have a substantial bio-load. Some models are better than others, but most available today will produce good results. Over skimming can remove beneficial organisms, so running a skimmer continuously in a marine planted tank is not desirable as it will remove too many nutrients that the plants need to grow.

Biological Filtration

The best form of biological filtration for any marine system is the use of live rock or coral rubble. Live rock is full of organisms and bacteria that naturally filter aquarium water by consuming and converting nutrients and breaking down harmful elements through denitrification. Live rock is natural, attractive and provides a surface for marine plants to anchor and thrive. Uncured live rock is the best choice if it is cured properly because it will contain much more life than cured live rock. Aqua cultured live rock, although sometimes more dense than wildly collected rock, offers the hobbyist with the most variety of marine life, including beneficial bacteria, invertebrates and macro algae. External or internal pumps provide water circulation which is important for live rock to function. The size of the system and its inhabitants will dictate how much flow is ultimately needed.

Chemical Filtration

There are three main types of chemical media that are used to filter aquarium water. They are activated carbon, phosphate absorbing, and nitrate absorbing media. The use of activated carbon to chemically filter aquarium water has long been the preferred choice in both fresh and salt water aquariums. Although it can be useful in a marine planted aquarium, carbon should be used sparingly as it also can remove needed compounds and nutrients from the aquarium water. Phosphate and nitrate removing media can be used when levels get out of control but should be removed at the recommended interval so that the nutrients do not leach back into the aquarium after they have out lived their ability to absorb nutrients. A deep sand bed can also be utilized in a planted tank to control the amount of nitrate through the formation of anaerobic bacteria deep within the sand bed. Most deep sand beds need to be 6″ or so to be effective however as too little depth can create a toxic mess. Overall nitrate is needed by all marine plants and depending on the rate of growth its presence in low levels is beneficial to the health of the system.

Water Quality

Aquarium water for use with a marine aquarium is made by dissolving salt mix with either purified water or tap water. The composition of household tap water varies greatly depending on what region the hobbyist resides. Tap water can be hard or soft, alkaline or acidic and contain variable amounts of other elements. Most salt mixes in the industry are composed of all naturally occurring elements found in natural seawater. Purified water is the best choice for any marine system as it removes 99% of contaminants and nutrients from the water. Sources of purified water include demineralized, reverse osmosis/deionization, and distilled water. In some cases tap water can be treated chemically and used in a marine planted aquarium. This is done with large scale aquaculture as the excess nutrients are quickly consumed by the plants. For most aquariums, purified water is the best choice and will help to drastically reduce unwanted algae blooms and harmful elements. If you live near the ocean, natural seawater can  be used, but can often add unwanted bacteria, pathogens and free floating algae to an aquarium if not treated. This can cause problems long term. Water changes are very important when maintaining a marine planted aquarium and help to remove nutrient rich water and replenish elements lost that were absorbed by the plants. The buildup of sediment on several species of macro algae such as Botryocladia can be avoided by regular water changes, increased flow and mechanical filtration methods.

PH

Natural seawater has a PH of 8.4. While most marine plants and organisms can survive in a wide range, it is best to strive to maintain a level as close as possible to natural conditions. An elevated ph can help reduce the growth of certain micro algae as many prefer a more acidic environment. 

Alkalinity

Alkalinity is the measurement of water’s ability to neutralize acids. The alkalinity of sea water keeps ph stable and a drop in alkalinity will lead to an eventual drop in ph. Most aragonite sand and salt mixes are sufficient to properly buffer aquarium water containing primarily marine plants. Again, water changes are essential for optimal health in any marine aquarium.

Temperature

Most tropical species of marine plants can survive in a wide range of temperatures from about 72 degrees to 86 degrees. Some species found in both tropical and sub tropical environments grow in seasons however and have a distinct preference for certain water temperatures. The green macro algae Ulva is one such algae that prefers cooler water temperatures and will not survive long in any aquarium above 80 degrees. Sea grasses begin a dormant stage when the water temperatures are in the low to mid 60’s and although remain alive, they will not grow. In the marine aquarium a range of 76 to 80 degrees is acceptable and should not present any problems for most tropical and sub tropical macro algae and sea grasses.

Specific Gravity

Slight differences in salinity or specific gravity has no negative effect on the photosynthesis and growth of marine  plants. Many varieties of sea grass can adapt to very large swings in salinity in their natural environment. The change however, must be gradual, as a drastic change in salinity can cause most marine macro algae to undergo the process known as sporulation. When adding fresh water to an aquarium containing marine plants, especially Caulerpa, be careful not to change the overall salinity of the tank too quickly. Specific gravity levels in a marine aquarium are normally 1.024 – 1.026, but marine plants can survive in slightly higher ranges if desired.

Water Circulation

The ocean is a dynamic and constantly changing environment, currents, tides and storms produce enormous amounts of exposure to plants, coral and fish. Water movement is very important for the growth of all marine plants in the aquarium. It aids in the removal of sediment, prevents some epithetic growth and provides increased diffusion of nutrients. Species such as Halymenia greatly benefit from strong flow to maintain their slippery fleshy fronds. How much flow is needed depends on the size of the system, but in general most plants can handle large amounts of movement.

They’re many suitable substrates for growing marine plants in the aquarium. The composition, depth and size of the substrate used is largely based on the individual species of macro algae or sea grass desired. Many commercial products are available to hobbyists for use with marine plants, but most are marketed for the refugium. Although macro algae does not derive any nutrients directly form the substrate, with the exception of sea grass, some type of substrate is usually needed for most species so that they can readily attach themselves. By far, the most popular substrate is the use of a fine grade aragonite sand at varying depths of up to 6” or more. Fine grade sand is readily colonized by most all Caulerpa species and is generally the easiest to maintain. There are also proven benefits to providing a deep sand bed to reduce nitrates and to culture marine fauna, but macro algae only require about 1” or less to attach and grow. Sea grass, however, does require a deep sand bed as its root system can extend quite deep, as much as 12”.

Careful attention should be taken to not introduce substrate to the aquarium that is too compacted, such as silica or quartz sand as this will most likely cause a dense anaerobic layer in the sand bed that can be toxic to tank inhabitants if disturbed. If a mixed macro algae and sea grass system is desired, it would need to devote some portion of the aquarium to a deep sand bed in order to successfully grow vascular plants. For the most part, a mixture of substrates will create an environment suitable for the addition of most any species desired. Most commonly available substrates are composed of variable amounts of aragonite and/or calcite. Aragonite is beneficial in its ability to properly buffer the aquarium water, helping to maintain both ph and alkalinity. Smaller grain sizes dissolve faster while coarse media such as crushed coral is much slower to break down requiring a higher ph to dissolve. Marine plants that do well in a fine to medium grade aragonite sand include most species of Caulerpa and calcified algae such as shaving brush & mermaids fan, as well as sea grass.

Coarse media such as crushed coral, shell or live rock rubble can also be used to anchor marine plants and is a good choice if a deep sand bed is not needed, especially in the refugium. The only drawback to using coarse sand/rubble is that it tends to collect detritus and sediment, often becoming a nutrient trap over time. In marine plant dominated aquariums this can be an added benefit however, as high levels of nutrients are needed for long term success. Some invertebrates are better suited to this environment, such as amphipods, while other soft bodied invertebrates desire a less abrasive environment. Most varieties of red and brown macro algae grow on rocks and hard bottom habitats in their natural environment, so a coarser substrate is more suited for anchoring. Marine macro algae such as Gracilaria, Botryolcadia, Sargassum and Halymenia can be glued or placed between rocks/rubble and will readily attach themselves. Most all macro algae are very adaptable, and will grow free floating or attach to most any surface, including substrate, live rock or even the sides or bottom of aquariums.

During the early 1990’s, mud filters began to gain in popularity for use in the refugium. Several manufacturers began offering a product that would duplicate tropical coastal environments, such as lagoons and mangrove habitats. These products claim to provide a variety of trace elements including, calcium, iodine, strontium, iron, and free carbon. The idea behind the “mud” was to provide a replenishing source of nutrients by slowly releasing them into the aquarium water. These types of substrates can be problematic long term as they will often become acidic and can effect the ph of the aquarium.

Keep in mind that in any macroalgae dominated system, any type of substrate will eventually get colonized with organic material and will need to be either removed or siphoned off the surface. Limiting the overall depth of substrate in both the refugium and or aquarium can make it easier to maintain the health of the sand bed. Some hobbyists even favor a bare bottom system with no substrate and only live rock for filtration where the detritus and sediment can be easily siphoned out.

Macro algae are much more diverse than vascular or terrestrial plants in their ability to uptake and process nutrients. They generally require a larger range of nutrients in an inorganic form than vascular plants do, but are able to derive a few essential nutrients from organic compounds such as some aquarium substrates. Few studies have been done on individual species of macro algae to determine which major and minor nutrients are essential to the plants survival and growth. This is due largely to the fact that natural seawater is used in most research and aquaculture production, which typically contains such high concentrations of the major and minor nutrients needed for plants to grow that specific data is never collected. However, it is commonly accepted that macro algae and sea grasses need the same essential elements as higher plants do. Unlike vascular plants, marine macro algae must be supplied nutrients through the water column and not through the substrate. This is achieved by providing all needed elements through the aquarium water.

Macro Nutrients

The macro nutrients, or primary nutrients, that marine plants need to achieve photosynthesis are: nitrogen, phosphate, potassium, sulphur, calcium, magnesium and carbon. Some marine algae that is heavily calcified, such as Halimeda optunia, need large amounts of calcium to grow. These plants in turn produce calcium based sand as a byproduct, which accounts for the majority of all Caribbean sand.

Nitrogen

Nitrogen is one of the major nutrients required by all plants and algae, both aquatic and terrestrial. It is used by the plants or algae in the production of stored proteins. Marine plants take up nitrogen in several forms, some more effectively than others. In the aquarium they include ammonia, ammonium, nitrite and nitrate. Nitrate is preferred among all marine plants and is a readily available nutrient in most aquariums. In most marine planted tanks and refugiums there is usually sufficient amounts of nitrates available in the water column due to the nitrogen cycle and fish waste to sustain small populations of plants without adding any additional nutrients. However, in heavily planted or sea grass dominated systems it will become necessary to keep nitrates elevated just enough to encourage growth. It is commonly suggested that a range of 5-10 ppm of nitrates is acceptable in marine plant dominated systems, perhaps more in more densely populated systems. Nitrate can be added as a supplement such as KNO3 (potassium nitrate) or CaNO3 (calcium nitrate) in dry form or premixed as a liquid. Another alternative is to use treated tap water without removing the nutrients. Great care must be taken with any periodic dosing as it can be harmful to both the plants as well as fish and invertebrates in the aquarium.

Phosphorus

Phosphorus is another important nutrient that marine plants need to grow. Marine plants readily absorb phosphorus in the form of phosphate (PO4). Phosphorus can be a limiting nutrient in the growth of marine plants but it is usually sufficiently present in the aquarium due to the addition of fish food, through detritus buildup and fish waste. In comparison with nitrogen, marine plants absorb far less phosphorus so care should be taken to limit the amount of phosphate in the aquarium Phosphate levels should be maintained below 0.07 ppm to rule out as a limiting nutrient. Dosing can be detrimental, causing algae blooms.

Potassium

Potassium is absorbed by marine plants as an ion from aquarium water and is generally available in sufficient amounts in most salt mixes and tap water. Potassium is a key component that is used for photosynthesis in marine plants. Dosing is generally not needed or required.

Sulphur

Sulphur is used by marine algae and plants in the production of amino acids, proteins and chlorophyll. It is generally present in sufficient amounts in both salt mixes and tap water. Sulphur can be toxic in large quantities so it should never be added as a fertilizer to the aquarium.

Calcium

Calcium is a very necessary element for all marine plants, as it is used in the formation of cell wall structure. As mentioned earlier, some macro algae such as coralline and calcareous algae readily absorb large amounts of calcium and are composed of almost pure calcium carbonate. Calcium, alkalinity and ph are all directly connected to each other, as the availability of carbonate mostly depends upon pH and alkalinity levels. So it is important to keep all three at acceptable levels so that calcium carbonate is freely available to the plants. Ideal dosing ranges are 7-10 DKH alkalinity, 8.4-8.5 ph and calcium levels between 380-450 ppm. Most commercially available products offer a simplified solution to maintaining the balance between alkalinity, ph and calcium levels. Calcium reactors can keep calcium levels high on a constant basis so are a welcome addition to any aquarium containing marine plants and invertebrates. Not only will keeping the ph and calcium levels high in a planted tank produce healthy plants, but the amount of micro algae will decrease as well.

Magnesium

Magnesium is another element that aids in the formation of cell wall structure within marine plants and especially coralline algae. It is often directly proportionate to the calcium levels found in both salt mixes and tap water. Because magnesium is an ingredient in most commercial salt mixes it is not normally necessary to dose this nutrient. However, magnesium will be depleted quickly with the formation of calcium carbonate in both plants and encrusting algae and needs to be monitored periodically. A target range of 1250-1350 ppm is sufficient for most marine aquariums containing calcareous and coralline algae.

Carbon

Carbon is used by all living organisms in varying amounts and is particularly important in the growth and structure of vascular plants. Plants obtain carbon from carbon dioxide, which is turned into oxygen through the process of photosynthesis. Most species of sea grasses can absorb large amounts of carbon from the both their roots and leaves, while macro algae are thought to need varying amounts depending on the species. It is generally accepted that the aeration/circulation provided by the filtration system creates enough free carbon to satisfy the needs of marine plants. The process of introducing carbon into the aquarium water through carbon dioxide fertilization does little to help in the growth of marine macro algae, but it would benefit a sea grass dominated system. However, the danger of a drastic fall in ph due to over saturation of carbon dioxide could be harmful and unproductive at best so it is seldom done in the marine aquarium hobby.

Minor Nutrients

The minor nutrients marine plants need to grow are: iron, manganese, copper, zinc & molybdenum, boron, iodine, bromine. These nutrients are normally needed in very small amounts so are often referred to as “trace elements” . Most commercially available salt mixes contain all of the minor nutrients needed for marine plant growth, so they are generally replenished by regular water changes.

Iron

Iron is an important micro nutrient absorbed by marine plants and is used in respiration and photosynthesis. The most readily absorbed form of iron is iron chelate. It is available in both dry and liquid forms and can be added safely to most aquariums without damage to its inhabitants. It is unknown how much available iron is used by marine plants but studies have shown that plants benefit from improved growth and color in systems that keep it at acceptable levels. There is some debate as to the quantity that should be dosed but most hobbyists add enough iron to rule it out as a limiting nutrient. 

Manganese

Manganese is absorbed as an ion by marine plants and is used in photosynthesis. It is not normally a limiting nutrient in most marine aquariums as it is present in both salt mixes and tap water.

Copper

Copper is absorbed in very low concentrations as an ion and is used in respiration by marine plants. Marine invertebrates are very sensitive to copper so it should never be added to the aquarium water as it is present in significant amounts in both salt mixes and tap water.

Zinc

Zinc is used by marine plants in the formation of chlorophyll and is present in both substrates and tap water. At high levels it is very toxic and should never be added to the aquarium water.

Molybdenum

It is unclear what role this element plays in the growth of marine plants. In terrestrial plants it is used by the plant to break down nitrates into ammonium to be used as a source of nitrogen. Trace amounts are present in salt mixes and tap water.

Boron

Vascular plants require small levels of this nutrient for cellular membrane function, root growth and flower production. Boron has been shown to be essential for some marine algae, but not for most macro algae. Most salt mixes and tap water contain significant amounts necessary for the algae and plants that utilize them.

Iodine

It is believed that some varieties of red and brown macro algae require iodine and bromine as essential nutrients for growth. It has an obscure place in the marine aquarium hobby but is available as a supplement for species that require it.

Vitamin B12

Several species of macro algae utilize Vitamin B as an essential element of growth. It is also thought to be necessary in the growth of several sea grass species including turtle grass. Not much is know on the quantities needed as most prepared salt mixes have sufficient amounts present.