A Complete Guide to Coralline Algae

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Algae is often thought to be the bane of any aquarium enthusiast’s tank—and for good reason.

Large amounts of it can produce too much oxygen or release too much nitrogen back into the environment when it dies, creating an unsafe chemical imbalance that could kill everything inside your tank.

coralline algae

Not all algae are bad algae, however. Take coralline algae, for instance. This type of saltwater aquarium algae is not the typical green, brown, or red fuzz your filter needs to clear out every so often. Instead, it’s a colorful and ultimately necessary part of any tank’s reef system.

Let’s take a look at what exactly these algae are, how to grow coralline algae of your very own, and the many beautiful colors these algae come in.

What Is Coralline Algae?

Coralline algae are a special kind of red algae that belongs to the order Corallinales. It is usually pinkish or red in color, though some other species become an extravagant purple, yellow, blue, white, or gray-green that would make any tank pop with vibrant colors.

Coralline algae grow in a variety of different ways in nature, but aquarium enthusiasts should look into growing crustose coralline algae or CCA for short. This species has solid limestone deposits within its cell walls that eventually build up a tough aragonite crust over any available part of a reef.

The algae then continue to stack on top of itself or anywhere else along the reef, forming a strong foundation where precious corals (and the types of fish that live within them) then have room to grow.

Essentially, these algae act as a cement of sorts, to stop any budding corals from breaking up or coming apart from the reef during any sort of intense wave activity in nature.

Coralline algae are quite the hardy species, found in pretty much every ocean in the world. They can be mainly found in intertidal zones exposed at low tide and will continue to grow all the way down to depths of 1,000 feet.

They can withstand many turbidites, meaning they can survive any marine environment that receives sunlight, and holds a wide variety of different nutrient concentrations inside itself.

Perhaps the most surprising fact about these algae is that, no matter how much of it you have in your tank at home, it will not put your fish or aquatic plants in any danger whatsoever.

In fact, these special algae are an all-encompassing treat for any kind of saltwater (and some freshwater) fish you might have. It acts as a plentiful food source for reef dwellers and can house many forms of invertebrates due to its knobby protuberances.

Coralline algae’s versatility and bright colors will create a truly outstanding aquarium, but just how do you grow it in the first place?

Coralline Algae Growth

You might think to handle a tank full of these algae is a feat only experts should attempt – but it’s surprisingly simple. You could find yourself building up a healthy reef system even without prior experience!

coralline algae growth

Of course, you need good coralline algae growth built up within your tank to establish a reef in the first place.

There are several ways to start growing coralline algae. Unfortunately, it does not grow organically in your aquarium as other types of algae do, so you will need to manually introduce it into your aquarium’s ecosystem.


This is typically done through installing a coralline algae-covered live rock, coralline algae scrapings from some other tank, or through commercial coralline algae starter packages like ARC Reef’s Purple Helix coralline algae in a bottle.

High quality live rocks will usually house dozens of different coralline algae species of varying textures and colors, all of which compete for space on the single live rock.

The more of these algae you introduce to your tank, the more you will see them grow over the live rock they originated from, as well as on coral skeletons, shells, glass, plastics, other species of algae, the other surrounding substrate, and even along your aquarium’s walls.

Coralline Algae Growth Speed

Coralline algae tend to grow at an extremely slow rate of 0.4 to 1.2 inches (or 10 to 30 millimetres) per year, so you need to have patience.

The growth speed also depends on grazing fish to clear out any rapidly growing seaweeds, which otherwise smother both the coralline algae.

Clean coralline algae are also essential to keeping these crusts and the corals that rest on them alive.

Growth Patterns

There are two types of coralline algae growth: geniculate (or articulated) coralline algae and nongeniculate (or nonarticulated) coralline algae. The main difference between these two types lies in how they grow in your tank.

Geniculate (or articulated) coralline algae tend to sprout out like a tree with surprisingly flexible branches, due to their noncalcified sections. Some of the branches may even look like miniature castle towers when they are bunched closely together.

coralline algae
By: Derek Keates (Creative Commons Attribution-Share Alike 2.0 licence)

Nongeniculate (or nonarticulated) coralline algae acts much like any other algae, meaning that they will grow on pretty much any surface (including rocks, shells, sea grass, or even coral skeletons) and look like a flat sheet or a hard crust when fully formed over that surface.

This type produces critical chemicals that promote the larvae of certain invertebrates to settle inside them for protection. In fact, sea urchins, chitons, and limpets would not continue to exist today if not for the protection given by these coralline algae formations.

Though both types grow very slowly, they will still manage to prevent most other species of rapid growth nuisance-algae (including hair algae, green algae, diatoms, and mat algae) from growing over them or near them, so long as the reef environment maintains the proper water chemistry.

This is because most coralline algae species are epiphytic, meaning they have the chemical defences to fight off other nuisance-type algae.

If they lacked this quality, they would quickly be overwhelmed and suffocated by more invasive species.

This video goes into more details on Coralline algae growth.

Parameters for Growing Coralline Algae

Much like any aquatic life, coralline algae depend on a stable environment to survive.

It is always a good idea to regularly check your water parameters to ensure the appropriate needs are met. This can be accomplished by manually monitoring your tank and by testing your water for a good balance of chemicals.

  • Nitrates: You should keep your nitrates below 5 ppm.
  • Phosphates: You should keep your phosphates below 0.25 ppm.
  • Magnesium Levels: You should keep your magnesium levels anywhere between 1,300 to 1,380 ppm.
  • PH Level: Your aquarium’s pH level should be maintained between 8.1 to 8.3. Keep in mind that you should always test your aquarium water’s pH levels at the same time of day, as pH levels tend to fluctuate throughout a 24-hour cycle.

KA Levels

You need to keep a KA level of 2.8 meq/L for alkalinity and carbonate hardness (which is the concentration of carbonates and bicarbonates in your tank system). This level can be plus or minus up to 0.14 meq/L, though no higher or lower than that.

Basically, maintaining the correct KA level in your tank will also stabilize the pH of the water, which will keep your fish, coralline algae, the growing corals, and the reef system happy.

Water Changes

It is best to have more frequent water changes, replacing small amounts of water, rather than water changes that take place less often but replace larger amounts of tank water.

This will prevent your fish and the coralline algae itself from going into shock at the sudden change to their environment.

You only need to do these water changes at least one to two times per month, though if you find yourself changing your tank’s water less frequently, then you may need to test and dose magnesium and calcium into the environment.

This is because coralline algae is a calcareous algae, which uses both magnesium and calcium to build up its solid structure. As such, it’s not able to reproduce without these crucial elements in the environment.


You need to keep your tank at a relatively stable temperature, as you would with any other tank.

In nature, coralline algae tend to grow approximately 10 times faster in tropical waters than anywhere near the Arctic or Antarctic.

purple coralline algae
By: Derek Keates (Creative Commons Attribution-Share Alike 2.0 licence)

Basically, you need to keep the tank between 78 to 81 degrees Fahrenheit, so if you have fish that do not live well in this kind of environment, it’s best to move them to a separate tank altogether.

To maintain this range, many experts recommend getting an accurate aquarium heater with its own separate temperature sensor.

How to Let Coralline Algae Grow and Still Keep Your Tank Clean

Once you get some decent coralline algae growth in your aquarium, turn off all your tank’s filters and skimmers, while leaving any powerheads running. This ensures it spreads out more evenly.

If you do not want any coralline algae clinging to the glass walls of your tank, take a single-edged razor blade and scrape them off whatever surface you deem necessary.

The water current that is generated by the running powerhead will then spread the scrapings to other parts of the tank, where they can continue to grow.

After leaving the scrapings to settle for about an hour or so, turn the skimmers and filters back on. This will keep the rest of your aquarium free from any dirt or other pesky species of algae that you definitely do not want accumulating.

You can also move the scrapings to another tank, growing even more of these algae there, if you wish.

Types of Coralline Algae

Red Coralline Algae

This is the most common color of coralline algae that can grow in your tank. The shade of red may differ from a faded pink to a more vibrant pinkish-red.

Ultimately, its final appearance and the intensity of its hue all depend on the type of live rock or other means you use to introduce these algae into your tank.

However, keep in mind that not all red algae in your saltwater tank are red coralline algae. They may actually turn out to be red slime algae instead.

These so-called “algae” are not alga at all, but cyanobacteria, which is widely considered to be the evolutionary link between bacteria and algae.

how to grow coralline algae

Cyanobacteria – or cyano, as it is often called – is one of the oldest life forms on Earth, with its origin dating back to 3.5 billion years ago. Mostly, experts just consider it another nuisance-alga, so you can feel free to clear it out with a filter or by manual removing it.

Red slime algae are typically a deep cranberry or red color. They have a slimy, stringy sort of appearance.

One way to tell the difference between these “algae” and red coralline algae is the fact that they will not crust over or harden once they grow over a surface. They may also have air bubbles sticking or forming on them, as they produce extra oxygen as a byproduct of photosynthesis.

Red slime algae will also grow much faster than your typical coralline algae, which means you should also clear it out as quickly as you can. Cyano starts out as a small patch in the sand or on your live rock, but if you do not pay it any mind, it will rapidly take over your tank when you are not looking.

Purple Coralline Algae

Purple (or any varying shades of it) is the second most common coralline algae color you might get. It is typically one of the more vibrant colors of this species, and adds a lovely aesthetic to your tank.

Here’s a video with more tips on caring for saltwater aquarium algae.


While plenty of algae in your aquarium can mean bad news, having coralline algae is a different story.

These algae provide so many benefits to your tank, it’s a wonder why more aquarium enthusiasts don’t take up reef keeping!

They are easy to keep, nice to look at and create both a healthy reef system and a better overall tank environment for all your fish.

Have you tried using Coralline algae in your tank?

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