Macroalgae Tank: A Complete Guide

Jennifer Doll

Jennifer Doll

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Are you looking for some excitement and color in your aquarium but don’t want a full saltwater reef tank? A macroalgae tank could be perfect for you.

These aquariums are not very common in the marketplace, but they’re simple and efficient in design. Many hobbyists seek the bright colors and exciting movements of coral, but macroalgae can provide the same benefits and appeal with less work.

Keep reading to learn how to set up a macroalgae tank and the best macroalgae species available for your saltwater aquarium!

What Is Macroalgae?

Macroalgae are regularly known as seaweed. This is a large group of macroscopic marine algae containing three major groups: Rhodophyta, Phaeophyta, and Chlorophyta.

Rhodophyta Spp.

Rhodophyta

Rhodophyta is red macroalgae. This is the largest group of macroalgae, containing about 7,000 different species.

These seaweeds can be identified by their red or purple coloration. 

Phaeophyta Spp.

Phaeophyta

Phaeophyta is brown macroalgae. Many of the species within this group originate from cold climates in the Northern Hemisphere, like kelp. 

These macroalgae usual have a brown coloration, but they can also appear green. 

Chlorophyta Spp.

Chlorophyta

Chlorophyta is green algae. Most of the species within this group originate from freshwater ecosystems.

These macroalgae can be found growing in extreme conditions, like deserts and hydrothermal vents.

Macroalgae vs. Nuisance Algae

At this point, you may be asking yourself why you would intentionally add algae to your aquarium.

Most hobbyists struggle with pest algae outbreaks, so what makes macroalgae any better? 

Micro and macroalgae are not all that different and behave similarly in an aquarium setting. Unwanted algae are only bad because it’s not attractive and can overrun your aquarium. 

Nuisance algae are very efficient at nutrient export, which can be a problem if you’re trying to grow other nutrient-demanding species. As we’ll discuss, marine macroalgae are also very efficient at nutrient export but are much more controllable and appealing to the eye.

Are Macroalgae Good For A Reef Tank?

Macroalgae are great for reef tank systems. Many hobbyists include macroalgae in their tank sumps for additional filtration. 

Macroalgae function in the same way that freshwater plants and marine corals do by nutrient export and introducing oxygen back into the tank. 

To grow, macroalgae need nutrients and light. In reef tanks, hobbyists need to control their nutrients and balance lighting to prevent pest algae from growing.

How To Set Up A Macroalgae Reef Tank

Setting up a macroalgae tank isn’t hard, but special attention needs to be given to the lighting. 

A macroalgae reef tank can be made from any tank size, though a larger tank will allow for better stability and will provide visibility to how nutrients move throughout the system. 

If you’re planning to keep macroalgae in a small or crowded tank, it may be necessary to dose nitrate, phosphate, or trace elements, like iron.

If planning to keep calcareous macroalgae, like Halimeda, then you may also need to dose alkalinity, calcium, and magnesium. 

Most macroalgae can withstand a medium to high water flow as long as they’re not being ripped off the rock. Many species of macroalgae live in tidal zones where they are subject to random waves and current conditions.

Macroalgae Lighting

Macroalgae are not all built the same. There are three different groups of macroalgae, coming from all areas of the world and conditions.

In general, red algae, Rhodophyta spp., do not need much light and can be kept under lights geared towards soft corals.

Green macroalgae, Chlorophyta spp., require a little more lighting and should be kept under bright conditions meant for large polyp stony, LPS, corals and small polyp stony, SPS, corals.

If you want to set up a macroalgae aquarium, it’s best to have a reef tank LED light meant to grow corals.

Not only will this provide your aquatic plants with the spectrum and intensity they need, but it also leaves room for growing other corals as well.

How Fast Does Macroalgae Grow?

Some types of macroalgae can grow very fast. Species like chaeto are especially known for growing fast under the right conditions. 

Because red algae grow in lower lighting, they can be the slowest to grow and least efficient at exporting nutrients. Green algae are much better at nutrient export and propagating than other algae.

However, calcareous green algae do grow slower than regular green algae because it needs to form a hard skeleton. 

Refugium 

A refugium is part of saltwater tank filtration, usually located in a sump under the tank or in its container. 

Refugiums are their own mini-ecosystems. Hobbyists throw substrate, sand, live rock, corals, and macroalgae into them for additional biological filtration.

The main goal of a refugium is to be a nutrient export through natural means. Refugiums also act as a safe place for copepods and other beneficial invertebrates to repopulate the tank.

A popular macroalga for the refugium is chaeto, Chaetomorpha linum. This type of macroalgae is fast-growing, nutrient-demanding, and easy to control. 

However, macroalgae are photosynthetic and need a light source. Luckily, chaeto does not need much light to be effective at removing nutrients.

For more information on refugium lighting, check out our top 5 refugium lights list for the best options available. 

The Best Macroalgae For Reef Tanks

Surprisingly, there are several different macroalgae species available in the saltwater aquarium hobby!

Macroalgae are relatively inexpensive but can be difficult to find at times. Macroalgae are not usually carried by most local fish stores so hobbyists will most likely find their desired species online. 

Here are some of the most common types of macroalgae to find in the display aquarium and for filtration purposes.

Chaeto (Chaetomorpha Linum)

Chaeto

Chaeto is one of the most popular and resourceful types of macroalgae, though it’s rarely seen in the display aquarium. Instead, chaeto is used in the refugium of the sump to absorb excess nutrients.

Chaeto is a great option if you’re looking for fast-growing macroalgae. However, this can also become a problem as it can quickly overtake the entire tank if left to spread.

Luckily, chaeto is pretty easy to prune as it grows in a concentrated ball. 

Ulva Spp.

Ulva

Ulva spp., also known as sea lettuce, is not the most popular green macroalgae available. Species of this broad-leaved macroalgae can be found in shallow waters all around the world. 

In the aquarium, sea lettuce is very adaptable and quick to grow, especially under strong lighting. Although it’s not a popular addition to the display aquarium, it can be used in the refugium for nutrient export.

Due to its size, it is relatively easy to prune and remove if needed.

Gracilaria Spp.

Gracilaria is the most common red macroalgae to find available. Because of their red primary color, they’re typically kept in the display aquarium.

Most times, different species of this macroalgae are sold under a general flat branch ‘Gracilaria’ common name. Sometimes, the exact species may be listed.

For example, here are a few known species of Gracilaria in the aquarium trade:

  • Flat branch Gracilaria (Gracilaria sp.)
  • Red ogo Gracilaria (Gracilaria parvispora)
  • Dragon’s breath/Pom pom Gracilaria (Gracilaria hayi)

It should be noted that some herbivores, like tangs, may eat any available Gracilaria.

Caulerpa Spp.

Caulerpa

The Caulerpa genus provides many green macroalgae options for hobbyists. However, these macroalgae can grow very quickly and need to be regularly trimmed.

Like freshwater plants, most species within this genus use runners to propagate, or a stem that branches out from the parent plant that can grow another plant.

The most popular species of Caulerpa macroalgae are:

  • Caulerpa prolifera
  • Cactus Caulerpa (Caulerpa cupressoides)
  • Caulerpa mexicana
  • Fern Caulerpa (Caulerpa sertularioides)
  • Grape Caulerpa (Caulerpa cupressoides var. lycopodium/Caulerpa racemosa)
  • Suction cup caulerpa (Caulerpa sp.)

If you’re looking for a species of Caulerpa that won’t take over the entire tank in a matter of weeks, then cactus Caulerpa is a great slow-growing option.

Halimeda Spp.

Halimeda

Halimeda, also known as the money plant, is different from the other macroalgae on this list. This green macroalgae is calcified and excretes a hard calcium carbonate skeleton, much like many corals do.

These macroalgae can be more sensitive to excess nitrates and phosphates than other species and can be slow-growing based on water parameters.

To get the best results, keep your calcium around 350-450 ppm with moderate lighting and moderate water flow

These are the most common Halimeda spp. available:

  • Carpeting Halimeda (Halimeda opuntia)
  • Halimeda monile
  • Halimeda incrassata

Blue Hypnea (Hypnea Pannosa)

Blue Hypnea is a popular macroalga due to its uncommon purplish-blue color. Because of this, these algae tend to be more expensive.

In addition, blue Hypnea can be more difficult and slow to grow than other macroalgae. They need moderate lighting and moderate water flow.

Blue Hypnea is recommended for hobbyists at the intermediate level due to their difficulty to grow and maintain.  

Shaving Brush Plant (Penicillus Spp.) 

Penicillus

The shaving brush plant is unique and not seen in many aquariums due to its singular appearance. These algae are named after their smooth handle and bushy bristle.

Shaving brush plants should be planted on a sandy substrate. They come from shallow waters, so strong lighting is preferred with moderate water flow.

Within this genus are pencil cap algae (Penicillus capitatus) and shaving brush (Penicillus dumetosus), which closely resemble the fanned macroalgae, mermaid’s fan plant (Udotea spp.). 

It should be noted that sea urchins have been known to eat shaving brush, though other herbivorous animals will leave it untouched.

Macroalgae Goes Sexual

Though there are more benefits to keeping macroalgae than cons, there is a possibility for them to go sexual.

This is the process of macroalgae releasing spores into the water column. This leads to incredibly fast dispersion and growth, which can take over a system if not maintained. Some hobbyists have compared this to dealing with Aiptasia, especially with fast-growing species.

However, not all macroalgae do this and there are some reasons they might decide to go sexual that include: 

  • Limited space: Macroalgae can grow quickly, leaving the immediate neighboring areas overcrowded. Once this happens, the algae will want to expand further but do not have the real estate. As a result, they’ll release spores to increase the odds of propagating new areas.
  • Limited nutrients and resources: this is similar to the idea of limited space but is not ideal for the macroalgae in an aquarium setting.

As resources and nutrients are depleted, the macroalgae can determine when it’s time to move on to another area that might have better prospects. 

In the aquarium, this can be ineffective as the spores can’t travel to more optimal locations. This can lead to the new macroalgae being unable to take hold and grow.

Most hobbyists don’t experience their macroalgae going sexual, but there are ways to reduce the possibility of it happening. 

If you have especially fast-growing macroalgae, then regular pruning and trimming are necessary. Not only do you risk the chance of the algae going sexual, but this can also take light and nutrients away from other animals and plants in the tank.

In addition, keep an eye on aquarium water parameters. If dealing with calcareous macroalgae, then calcium, magnesium, and alkalinity need to be monitored.

If you have a particularly fast-growing species of macroalgae, then nutrients will be drained much faster. Manual dosing and increased feedings are recommended. 

Final Thoughts

Coral reef tanks are highly desired in the aquarium hobby, but what if you could get all the movement and color of corals through less-demanding algae?

Macroalgae tanks aren’t commonly seen, but they’re effective for taking up nutrients, providing food for tank inhabitants, and creating an attractive and unique display tank.

If you have any questions about the types of macroalgae listed in this article, other less common species, or have had experience setting up a macro tank of your own, don’t hesitate to leave a comment below! 

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