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Is Green Coralline Algae Real?

Anyone who owns an aquarium will know how important it is to regularly monitor the algal behavior in the tank, and to watch for the appearance and disappearance of “good” and “bad” algae – but sometimes, it’s hard to tell the difference between the two.

If you have ever heard of green coralline algae, you may be wondering whether this is something that you want to see in your tank, or whether it could be dangerous to your aquarium’s inhabitants.

Being able to tell the difference between the various kinds of algae and accurately identify them will help you to keep your tank healthy and avoid issues occurring.

Coralline algae are usually red, and they are considered an asset in saltwater aquariums, partly because they will only appear in a tank that is mature and balanced.

They get into your aquarium via a live rock being placed in there, or they may arrive on a snail’s shell, and their presence is beneficial, helping to secure reef structures and outcompete the growth of nuisance algae.

Coralline algae are also attractive and colorful, so many people are pleased when they see them appearing in their aquariums.

They can be very vibrant, and will help to make your tank look finished and complete. Coupled with their cementing ability, these algae are certainly a great thing to find in your aquarium.

Can Coralline Algae Be Green?

Coralline algae are usually red, but it is possible for them to be green in some circumstances, yes.

However, green algae are slow to grow and will usually only form in concentrated areas where the conditions are particularly good for them; they will not spread to fill the entire tank, even if you do what you can to nurture them.

There are many other color variations, too, such as yellow, white, and blue, but the commonest colors are red, lavender, magenta, purple, violet, etc.

It is easy to misidentify green coralline algae, especially if you are a relatively new hobbyist and not familiar with the different kinds of algae.

Green coralline algae (like other kinds) must be introduced to the tank on a live rock or a snail; they will never form in the water of their own volition.

They also will generally only appear in tanks that are mature and that have very stable water parameters, so you will usually not see them unless your tank is at least a year old (although there are exceptions to this, and some people will see them within a few months of setting the tank up).

Green coralline algae are often very bright in color, and will spread across the rocks in your tank, or occasionally on the glass.

They may grow alongside other colors of coralline algae, and they are equally beneficial and desirable, so do not attempt to remove them from the tank.

“Coralline algae – note the green dead ones, possibly due to disease” by Derek Keats is licensed under CC BY 2.0. To view a copy of this license, visit

How Do You Care For Green Coralline Algae?

The key thing when trying to encourage green coralline algae is to keep your tank environment as stable as possible.

The algae will have formed because the conditions are right for them to thrive in, and therefore you want to maintain these conditions as far as you possibly can.

It is easy for a small change to upset the balance in your tank, so make sure you are regularly testing the water to check that the levels are all correct, and make swift adjustments if something has altered.

Keep your nitrate levels below 5 parts per million (ppm), your phosphates below 0.25 ppm, and the pH value between 8.1 and 8.3.

Be aware that you may need to add magnesium and calcium if you aren’t regularly changing the water in the tank; coralline algae need both of these things in order to keep growing, and will therefore die if they get depleted.

The temperature of the tank is important too, and should be kept between 78 and 81 degrees F.

The lighting is also key to this kind of algae, and consistency is again crucial.

The algae will not like light that is very strong, but they also won’t thrive if the light is weak, so you need to find a balance somewhere in the middle.

You need to ensure that the lighting reflects the movements of the sun as closely as possible, with low intensity lighting for some of the day, and more intense light at noon.

Is Green Coralline Algae Expensive?

It isn’t possible to buy green coralline algae specifically, and these algae are normally introduced to aquariums through either the purchase of live rocks or the introduction of snails, which may be carrying the algae on their shells.

Live rocks can be expensive, depending upon the supplier, but in general, a live rock will cost under $10.

It is possible to buy coralline algae (but not green coralline algae) in a bottle, and this will often be around $20, or a little more, but you should be aware that the algae will not thrive in your aquarium if the conditions are not right.

It is best to introduce green coralline algae by adding a rock or snails to the tank once you believe it is stable and capable of supporting this kind of algae.

Check all the levels and the temperature before doing this, and monitor them for a few weeks/months to ensure they are not fluctuating much. This will give the algae the best chances of survival.

It would be expensive to constantly add live rocks to your aquarium in the hopes of introducing green coralline algae, but if you ensure the tank is suitable, one rock may be sufficient.

Be patient and see if the algae appear and develop before you try again, and remember that these algae grow very slowly!


Green coralline algae is a beneficial and pretty addition to any aquarium, and will help to bring stability to your rocks, as well as adding beauty and color to the display. However, it isn’t easy to get these algae established, and they will usually only survive in a stable and mature tank that is free from major fluctuations in terms of temperature and lighting. Keep an eye on your tank’s parameters and only introduce live rocks or snails when you are sure that the tank is ready for them.