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Coralline Algae: Everything You Need to Know

Coralline Algae is often thought of as a mere nuisance to reef keepers looking for clean walls free of coral competitors. But in truth, these algae are as important as reef corals themselves in promoting a healthy reef ecosystem, both in aquariums and in nature. Being so misunderstood, it is often seen as a pest to aquarists looking for nice, spotless tanks. But a spotless environment is rarely a healthy one…What does Coralline Algae have to offer the marine aquarist?

Understanding Coralline Algae

Coralline algae are red algae that belong to the order Corallinales. What makes them distinctive is their crusty calcareous skeleton. Like corals, Coralline Algae absorb calcium carbonate from the water column and deposit it into stratifying layers that form a fortified permanent home.

And again, just like corals, Coralline Algae form their calcareous skeletons into all kinds of fanciful shapes that serve a few known and several unknown purposes.

coralline algae on rock

One main purpose is to encourage the growth and reproduction of marine invertebrates that feed on green algae, such as abalone and sea urchins. Sine Coralline Algae spreads much more slowly, having a healthy population of grazers helps clear the way for their arrival.

In the aquarium, Coralline Algae also act as direct competitors to nuisance hair and bryopsis algae by covering available living space and acting as sinks for phosphates, nitrates, and other fertilizers.

There are over 1600 species of Coralline Algae that have been formally described. But the average aquarist need not be too worried about identification since even expert phycologists (scientists who study algae) have immense trouble telling many of them apart.

Most Coralline Algae are varying shades of pink. But there are several that are yellow, green, or amber in color. Being plant-like, they have chloroplasts and use photosynthesis to fuel their sugar production. They are all part of an ancient lineage that’s been working in tandem with corals for over 500 million years to build reefs for diverse animal and plant species!

Is Coralline Algae a decorative reef inhabitant or a pesky nuisance in need of control? To cut to the chase, that’s really up to you. Therefore, we will discuss both how to care for Coralline Algae in ways that help it thrive as well as how to control it.

Elimination is next to impossible once you have some. But remember that Coralline Algae thrives in the same conditions as SPS corals and LPS corals. Its presence is a sign of reef health, even if it’s not always appreciated. So let’s take another look at Coralline Algae, to help you make up your mind…

Caring for Coralline Algae

Most aquarists have a run with Coralline Algae at once time or another. But how did it get there in the first place?

How Does Coralline Algae Get Into My Aquarium?

Coralline Algae isn’t too difficult to get started inside an aquarium but once it does it can be a real hassle to get rid of. Since it’s an encrusting algae it doesn’t occur in thick concentrations in the water column unless you’ve just spent time scraping your aquarium walls of thick encrustations.

That’s one way an unsuspecting reef or marine fish keeper might get Coralline Algae from a retail store. Powdered Coralline Algae in the water column that then finds its way into a bag with a new fish or invertebrate purchase absolutely will form colonies in their new home.

Another common way for Coralline Algae to arise is through the purchase of corals and live rock. Coralline Algae is part of the ecosystem that grows on uncured live rock and are both a blessing and bane as a result. After all, there is always an element of surprise when it comes to buying marine live rock. Another blessing is that you may also find purple, green, or yellow Coralline Algae strains that are significantly more beautiful than the standard pink variety.

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That said, if you don’t want to leave things up to chance, you can easily introduce Coralline Algae into your aquarium. Fresh scraping from a tank that already has some will thrive in a new aquarium as long as you have conditions suitable for stony corals (see below).

You can also buy both pink and purple Coralline Algae bottled nowadays! This has the added advantage of knowing precisely what species you have on hand as well as preventing hitchhikers from coming along for the ride.

Just keep in mind that you’re buying living, photosynthetic organisms. That means you have roughly 2 weeks to get your freshly produced Coralline Algae into your aquarium. Without light and a place to attach to, the bottled algae will eventually die. ACR Reef’s Coralline Algae also includes nitrifying bacteria for a double dose of beneficial microorganisms to get your reef up and running!

Water Conditions

As one of the most important reef building organisms, you’ll need to provide similar conditions to help grow Coralline Algae. That means temperatures of 72-80℉ for most species and a pH of 8.0-8.24.

The specific gravity (salinity) should remain at 1.023-1.025 and levels of nitrate should remain less than 5 ppm (to prevent nuisance algae from overwhelming it). Phosphates should likewise remain at low levels. In short, Coralline Algae needs the same conditions as hard corals when it comes to water chemistry.

This means you’ll also need to keep track of calcium levels. Stony corals and Coralline Algae thrive between a range of 350-450 ppm. Calcium, along with carbonate, forms the main structural component of their skeletons. Magnesium is also extremely important because it increases the saturation potential of calcium and carbonate in seawater.

Without high levels of magnesium (1200-1350 ppm), you’ll see a reduction in both calcium and carbonate, halting the growth of Coralline Algae. If you’re running a fish-only aquarium, reducing the levels of calcium, carbonate, and magnesium can slow the spread of Coralline Algae over time.

Coralline Algae Water Conditions:

  • Temperature: 72-78℉
  • pH: 8.0-8.24
  • Specific Gravity: 1.023-1.025
  • Alkalinity: 9-12 DKH
  • Calcium: 350-450 ppm
  • Magnesium: 1200-1350 ppm
  • Nitrate: 1-10ppm
  • Phosphorus: 0ppm

Should I Encourage Coralline Algae?

If you’re interested in the most diverse reef ecosystem possible, then you should encourage Coralline Algae to grow. Corals are shown to preferentially grow on live rock coated in Coralline Algae.

The algae also compete with nuisance forms and encourage the growth of grazing invertebrates to further keep pest algae in check. Coralline Algae will also shed its outer layers periodically to prevent nuisance algae from getting established.

Coralline Algae also acts as a binding agent for live rock and coral fragments, gluing together structural components so that they are less likely to come undone and collapse. However it’s worth mentioning that it isn’t too picky where it adheres to. It will coat your glass, all of your rock, and even your filtration tubing and other aquarium technology.

However many aquarists, myself included, find that to be an attractive bonus. It takes attention away from the glass, metal, and plastic components that clearly don’t fit with the organic forms of the reef inhabitants. It’s a living backdrop for your aquarium!

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Coralline Algae is also an excellent indicator species; a canary in the coal mine in case you have water quality issues. Since they need the same parameters that stony corals do, should you see a sudden slowing or dramatic decline in your Coralline Algae, you have a cue to start doing some water tests.

Calcium, magnesium, strontium, and carbonate levels need to remain elevated for Coralline Algae to flourish. And like stony corals, these algae thrive on stability. Rapid fluctuations of even beneficial parameters can cause them significant stress.

Downsides of Coralline Algae

Most of the advantages I laid out for you can also be disadvantages from a different perspective. The most obvious one is that Coralline Algae will simply spread once it’s established and there really isn’t any way to direct how it grows.

The majority are very slow growing and will only spread at a rate of ½ to 1 inch per year. Such a slow growing algae can easily be cleaned from the glass and equipment a few times a year. But occasionally, you may come across a pink variety with a faster growth rate – these are the nuisance forms that tend to be accidentally introduced from pet stores.

Its spotty, often messy appearance as its becoming established may not be attractive to you or more perfection-oriented reef keepers. If you prefer the polished look of a mature reef, complete with gleaming life-giving technology in the background, you’ll want to avoid Coralline Algae at all costs.

Also be aware that thanks to its hard calcareous skeleton very few creatures eat Coralline Algae. Parrotfish will but they have the downsides of also being willing to eat stony corals and tending to be large fish. Sea Urchins are the only animals that will reliably eat Coralline Algae and even then they will go for other forms of algae before turning to it.

Sometimes you’ll read about aquarists advocating for limiting light levels but Coralline Algae isn’t like other types. Anywhere sunlight penetrates (up to 1000 feet below the surface), Coralline Algae can grow. It will simply grow slower as light levels diminish.

Controlling Coralline Algae

We’ve extensively covered the benefits and downsides of Coralline Algae in your aquarium. Much like bristle worms and other unintended guests, they offer distinct advantages and disadvantages. So you’ll have to decide for yourself if they are a good fit for your aquarium ecosystem. But what if you’ve decided you don’t want the Coralline Algae you have?

Well, controlling its growth is your only realistic option because the majority of algae eaters won’t touch it. Lawnmower Blennies, Hermit Crabs, most Snails, Tangs…All of them prefer juicier varieties.

Black Nerite Snails and Sea Urchins are semi-reliably at consuming it. But they still prefer other forms of algae and will likely ignore Coralline Algae if they have access to green algae.

Scraping it by hand from the aquarium glass is the only way to keep it from covering over your view of the tank. But considering how slowly it grows it doesn’t need to be an arduous task. A quick pass with a glass scraper will easily remove tiny colonies. It’s once they’ve been allowed to form thick plates that you have to put in more effort.

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If you’ve ever been in the market for a used saltwater aquarium there’s a good chance you found one coated in Coralline Algae. That aquarist likely let the problem get out of hand and decided to pass it onto you. Removing thick crusts of Coralline Algae can be a hassle because it resists easy hand scraping.

Filling a spray bottle with vinegar is your best option here. The vinegar is a weak acid that eats away at the calcium carbonate buildup. Soak the areas covered in Coralline Algae thoroughly and wait up to an hour before attempting to wipe or scrape away the coated areas.

If you have equipment like pumps, tubing, or powerheads covered in Coralline Algae, you can also soak them in vinegar to ease the cleaning process!

But once you have it, the only way to be truly rid of it is to tear down the tank entirely and then dry it out. And once it’s dried, you’ll likely want to use new live rock as the spores may survive, moist in deep cavities, only to germinate into new Coralline Algae colonies once saltwater returns.

In my opinion, it’s much better to embrace Coralline Algae as an attractive, if occasionally tedious, resident of a healthy reef aquarium!


The jury is still out when it comes to whether Coralline Algae is a pest or attractive resident. That’s mostly up to you to determine for yourself. If you like seeing additional diversity in your reef tank, then you should allow it to flourish or even encourage its spread with the stable water conditions.

And if you’re not a fan of it, use the control methods listed above to keep it from growing out of hand. Or remember that prevention is the best medicine and inspect all incoming coral frags, and live rock for signs of Coralline Algae colonies.

You can also ensure that as little unfamiliar aquarium water as possible enters your system by using quarantine tanks and other intermediate steps for new fish and invertebrates!

Jason Roberts
About Jason Roberts
Jason is an aquarium fanatic that has been a fish hobbyist for almost three decades.

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