How To Grow Marine Macroalgae

Today I am going to talk about how to grow marine microalgae. Marin macroalgae is a group of multicellular and unicellular organisms that exist predominantly on coral reefs, oceans, seas, and coastal regions.

These algae are not microalgae or phytoplankton, the word itself “macroalgae” defines them as algae that are visible to the naked eye. They are very much like plants and in fact, they used to be deemed plants.

Interestingly, these plant-like organisms are cultivated in marine aquaria due to the numerous benefits they provide. A host of marine aquarists grow macroalgae in their display tank or in the refugium, and this helps to create a more natural, healthy, and attractive environment.

Apart from the usual reef tank inhabitants— corals, copepods, anemones, fishes, shrimp, snails, etc., there is always a place for a little bit of macroalgae in your reef tank.

Do not worry, marine macroalgae are not like nuisance microalgae species like hair algae that are dreaded because of their tendency to wreak havoc in saltwater aquariums.

With proper care and attention, macroalgae pose very little or no threat to reef tanks, and they are mostly cultivated for their decorative and purification attributes which are very much desired.

Benefits of Marin Macroalgae

  • Macroalgae is highly palatable and nutritious; this makes it a great food source for herbivorous fish, copepods, and other marine inverts. Also, macroalga is a good alternative to specially formulated feeds which clearly costs more to acquire.
  • Macros help to complement the aesthetics of saltwater aquariums.
  • Macroalgae provide a refuge and breeding place for copepods and amphipods to grow and reproduce.
  • They help to increase the dissolved oxygen levels of the tank water.
  • They are useful in nutrient sequestration; removing excess nitrate and phosphate levels in reef tanks, thereby improving the water quality and making the environment safer for inhabitants.
  • Macroalgae tend to outcompete nuisance microalgae species that often grow as films on surfaces. Macroalgae deprive them of nutrients, light, and space to thrive.
  • They provide cover and dense hiding places for fish and other species, hence decreasing their stress levels and increasing quality of life.
  • Since a huge variety of macroalgae are easier to care for and able to tolerate changes in salinity, pH, and temperature better than corals, they are more ideal for beginner aquarists that may not be able to keep the latter due to its requirements.

Types of Macroalgae

There are over 10 000 macroalgae species. They are classified into three groups based on their coloration, include, for example:

  • Green macroalgae (Chlorophyta)
    — Species: Caulerpa, Codium, Ulva, Halimeda, Chaetomorpha, Udotea.
  • Red macroalgae (Rhodophyta)
    — Species: Gracilaria, Halymenia, Botryocladia, Coralline algae.
  • Brown macroalgae (Phaeophyta)
    — Species: Sargassum, Hormosira banksii, Durvillaea, Ecklonia, Dictyota.

Note: Brown algae are not really that popular in reef tanks because of their size in preferences for colder water.

Common Species of MacroAlgae Cultivated in Aquariums


How To Grow Marine Macroalgae Chaetomorpha

Chaeto or Spaghetti Algae is the most manageable and most popular. Fast-growing green macroalgae are known for their ease of care.

This species grows as a dense mat, and it is very efficient at keeping the water clean by stripping the saltwater of excess nitrates and phosphates.

Ideally, Chaetomorpha will create hiding places for a lot of fauna in the tank, and they do require intense lighting to survive. Also, you are required to trim Chaetomorpha regularly to prevent it from overtaking the reef tank.

Note: It can be very finicky, especially in a newish tank or one with low nutrients. In addition, any dying Chaeto should be quickly removed from the tank. Do not try and save it, just start over with a new batch.


How To Grow Marine Macroalgae Caulerpa taxifoliaThese macroalgae can be very aesthetically pleasing. Caulerpa features different varieties with grape shapes, flat and feather blades.

They grow rapidly, require frequent pruning, and are likely to go sexual— releasing their spores in the tank water after reaching a certain mass.

Caulerpa species also contain toxic compounds that tend to ward off herbivores from nipping on them.


How To Grow Marine Macroalgae Ulva - sea-lettuce
Photographs © M.D. Guiry

Ulva (sea lettuce) is an excellent nutrient exporter and serves as food for herbivores and marine invertebrates.

This green macroalga is fast-growing and very easy to grow.

Ulva is able to tolerate changes in temperature, salinity, very low and very high light levels, and it prefers more current than most species of marine macroalgae.

It is a very nice-looking macroalga, the only problem I find with them is that it breaks apart very easily.

Red Gracilaria:

How To Grow Marine Macroalgae Red GracilariaThis is a popular red macroalgae species with cylindrical-shaped branches that form a bush.

Gracilaria contains the red pigment “phycoerythrin” which overshadows the green pigment “chlorophyll” hence its prominent red color.

Gracilaria is a great natural food source for herbivores, it grows rapidly and requires ample lighting to thrive. It requires moderate-high flow, moderate lighting, and thrives best when attached to rocks.

On the downside, Gracilaria can break apart pretty easily if you rough handle it. However, unlike Ulva and Caulerpa, it will not clog pumps.

Dragon’s Tongue (Halymenia):

dragons-tongue How To Grow Marine MacroalgaeThis is a type of red macroalgae, it features a bright red form with orange tips.

Dragon’s tongue is easy to care for, it prefers moderate light and flow conditions to grow optimally.


How To Grow Marine Macroalgae HalimedaHalimeda sp. is a calcareous macroalga touted for its decorative attributes.

This alga doesn’t do well in water with high nitrates, phosphates, and other elements. They need moderate to high lighting, and high calcium levels of calcium and magnesium to grow and maintain their calcified structure.

Halimeda is fairly difficult to keep in the reef tank.

Water Conditions

Here are the ideal water conditions for growing macroalgae in a reef tank:

Salinity: It is recommended to keep the salinity between 1.024 – 1.026; though some macroalgae species can tolerate large swings in salinity, others may not be able to withstand it.

Temperature: The optimal temperature range for keeping macroalgae is between 75 – 79 °F (24 – 26 °C), species like Ulva (sea lettuce) are capable of handling extreme temperature conditions.

pH: 8.0 – 8.3

Hardness: 8-11 dkH

Calcium: 400 – 450 ppm. Calcareous species like Halimeda require high levels of calcium.

Magnesium: This should be between 1250 – 1350 ppm.

Ammonia: 0 ppm

Nitrites: 0 ppm

Iron: 0.05 – 0.1 ppm

Phosphates: Below 1 ppm, but not less than 0.02 ppm.

Nitrates: 5 – 10 ppm

Flow: Water flow is dependent on the specific requirement of the macroalgae type. Ideally, a moderate flow is considered good enough for most species of marine macroalgae.


Macroalgae require moderate – high lighting for best growth, also, keep in mind that lighting needs vary according to species). T5 bulbs, metal halides or LED lights usually in the 6500k to 1000k range.

Light spectrum with red and blue range will benefit them most.

Most red macroalgae will thrive under moderate lighting and sometimes in low lighting (for example, Bortacladia do not want intense light), whereas green macroalgae prefer intense lighting.

Interestingly, the color of macroalgae may vary with different lighting intensities e.g. low light levels will trigger a deep red coloration in red macroalgae.

If you are looking for the light recommendation a sump, check AI Prime Fuge light (link to Amazon) or the Chaetomax light from Innovative marine (check the price on Amazon). These are recommendations of the AlgaeBarn (one of the leaders in this industry).

Also do not be afraid to ask questions! You can ask the shipper about the photoperiod and intensity of the lighting they used to be kept under and replicate that if it is possible.


Macroalgae can be introduced into different spots in the tank by attaching small portions/fragments to live rock.

Certain species of macroalgae thrive best in the sand, hence they can be placed directly on the deep sand bed. Fragments of macroalgae can be fastened onto the live rock with a coral frag glue or fishing line.

Notably, it may take several weeks to form holdfast tissue which allows them to stay affixed to surfaces.

Species like Caulerpa, Halimeda can be placed on rock or sand, whereas Gracilaria, Chaetomorpha, Ulva & Sargassum can be fastened on a rock or allowed to float/tumble on the water surface.

Additionally, Udotea and Penicillus can be planted on the sand, while other species like Acanthophora, Halymenia, Botryocladia, and Ochtodes should be grown on the rock.

Macroalgae can be obtained from untreated live rock. It is common to find live rock covered in small fragments of macroalgae, and such rocks can be introduced into the reef tank.

Alternatively, you can request fragments from fellow reef keepers, or order some from a nearby reef store.

Note: Sometimes it can be a real pain in the back to attach macroalgae to substrate or rocks. So, if it is your case, I would recommend:

  • using a rubber band (fishing line) for the rocks,
  • lightly bury in sand,
  • shove in a crevice.

It worked best for me. I tried to stick with super glue to rock but they did not attach.

Genus Rock Sand Float
Ochtodes Yes
Botryocladia Yes  
Acanthophora Yes
Halymenia Yes
Sargassum Yes Yes
Gracilaria Yes Yes
Caulerpa Yes Yes
Halimeda Yes Yes
Udotea Yes
Penicillus Yes
Ulva Yes
Chaetomorpha Yes

Feeding MacroAlgae Cultivated in Aquariums

If you find yourself having trouble getting macroalgae to grow, it is likely that at least one of the elements (calcium, magnesium, iodine, potassium, phosphate, iron, etc. with the exception of carbon) is limiting the growth.

This is crucial!

Remember that algae can grow only until their biomass is supported by the nutrients available from the system! 

Unfortunately, according to hundreds and hundreds of questions on forums and Facebook groups, it happens a lot especially with people who use macroalgae in their refugium.

Note: Keep in mind that Iron is the most important micronutrient. While Phosphate and Nitrates are the most important macronutrient that will help your algae to survive. It is both a blessing and a curse at the same time.

One of the biggest issues with macroalgae is the fact that they can burn themselves out really quickly. Macroalgae can grow really quickly and then suddenly starts to slow down and sometimes even die back within a week or so.

This is the clear indication that they have run out of certain elements (nutrition) they were using up and now they cannot grow any longer.

 As a result, we have to add phosphate and nitrate back into the marine tank!

Of course, it may seem very counter-intuitive to do that because we wanted to get rid of them in the first place and now we have to add them back.

Basically, it is very similar to if you had a freshwater planted tank. Everybody knows that they are beneficial for the tanks even though we usually use fertilizers from time to time.

So, treat the macroalgae the same way. In a reef tank, you need to follow a similar sort of regime in terms of dosing.

How Do Macroalgae Feed

Macroalgae absorb the nutrients only through the stolon or through the leaves. The nutrients removed by the algae are locked inside of the tissue. By removing/trimming macroalgae, we also remove those nutrients from our tanks.

These algae do not really draw nutrients from the roots. Therefore, there is no reason to think that an enriched substrate will do any good.

The reason is that macroalgae use roots (which are pretty small by the way) as a holdfast to whatever substrate they are trying to live on.

Why is that important for us?

It simply means that we have to use a liquid fertilizer. For example – Brightwell Aquatics Chaeto Gro (link to check the price on Amazon)

Therefore, when we see that your macroalgae start to grow slowly and/or turn a pale color – they do not have enough nutrients.

Dosing Macroalgae

If you are planning to grow macroalgae or keep a macroalgae tank, it is recommended to dose small amounts of nitrate, phosphate, perhaps potassium, and micronutrients through the week.

Precautions with Housing Macroalgae

Reproduction (sexual event):

Some species of microalgae (for example, Calera and Halimeda) are capable of reproducing through the release of spores. Here, the phase commences with the formation of gametangia either in or on the algae; these structures hold the spores.

The spores are released into the aquarium from the parent algae when the tissues lyse, break open, and die.

Macroalgae reproduce when their population can no longer be supported by the nutrients in the reef tank. Also, this event can be equally triggered by inadequate light, stress, or variations in salinity or temperature, as well as improper photoperiod.

The best way of preventing the occurrence of a sexual event is through regular pruning.

Notably, green macroalgae are known to exhibit signs of sexual events. For instance, Caulerpa and Halimeda will bleach slightly and display numerous green dots in their surface just prior to the release of spores. Therefore, any macroalgae found with these spots should be removed from the aquarium immediately.

In a situation where a macroalga succeeds in releasing spores into the water, the aquarist should take action instantly by carrying out several partial water changes to help clear the decomposing tissue and spores from the tank water (as this may raise the nitrate and phosphate levels).

Furthermore, carbon media can be added to the filter and additional aeration devices may be introduced to help save the life of tank inhabitants.

Compatibility with Fish and Inverts:

Keep in mind that not all fish and invertebrates are compatible with macroalgae.

Herbivorous species like tangs, rabbitfish, sea urchins, dogface puffers, and angelfish will devour macroalgae in the tank regardless of how often you feed them.

Be very careful with emerald crabs and, in some cases, hermit crabs. Although some aquarists have not had any problems with hermits there are also some negative reports.

Most saltwater snails are usually safe to keep with marcoalgae. However, I also heard that some hobbyists complained that they eat scroll algae and sometimes Red gracilaria.

An example of mostly safe snails:

Personally, I would avoid:

These snails can be too indiscriminate in what they eat.

So, except you don’t mind such species eliminating the macroalgae in your aquarium, it’s best not to have these macroalgae eaters.

Another option is to have only calcareous macroalgae species which the herbivores will see unfit to eat.

Carbon dioxide:

Just like all aquatic plants do, Macroalgae produce oxygen in the presence of ample lighting. On the contrary, it will uptake oxygen and release carbon dioxide in the absence of light.

In situations where the macroalgae releases spores or light supply fails for long periods (dark hours), this prompts an increase in carbon dioxide which will alter the pH of the tank water.

To minimize this potential risk, many aquarists run a reverse light cycle in their refugium, and this helps stabilize the pH. Another way could be to combine CO2 infusion with calcium carbonate in a vessel (calcium reactor).


Choose only reliable suppliers, it will reduce the risk of introducing pests, diseases, and parasites in your tank.

Unfortunately, it can be risky to dip macroalgae as we do with corals in reed tanks and plants in freshwater tanks. Instead, it will be better to quarantine them and physically remove any pests you see.

Tip: Use a new growth on macroalgae when you decide to stock your refugium. This new growth will be the cleanest of all, so you will decrease the risk of contamination of your tank.


Under good conditions, macroalgae can be very prolific.

That is why it is recommended to use a separate refugium area where you can grow macroalgae for nutrient control without any risk of overcrowding and choking the corals for space.

New Tank

If you decide to try some macroalgae in your marine system you should already have elevated nitrate and phosphate levels.

This is especially important with a new tank. If you add them too soon, your nutrients may go too low and it will lead to problems.

In Conclusion

Corals are not the only way to make your marine tank look nice and beautiful. Macroalgae are the easiest thing you can do to help clean the tank. 

The addition of macroalgae is a great way to introduce a variety of colors and looks to your reef tank. There are lots of marine macroalgae to choose from, and if you are a beginner, it is best to avoid species that will easily go sexual.

With this guide, you should be able to cultivate and care for suitable species of macroalgae in your main display tank or refugium.

Lastly, do remember to keep an eye on the macroalgae, perform regular trimmings, and maintain good water conditions to ensure its survival.

Happy reef keeping.

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