Red Algae In Saltwater Tank: Remove, Control & Prevent | Aquascape Addiction

Red Algae In Saltwater Tank: Remove, Control & Prevent

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Want to know why there is red algae in your saltwater tank? and how to remove, control and prevent it? this post has the answers.

Red Algae In Saltwater Tank: Remove, Control & Prevent

Red algae growing in your saltwater fish tank can be a really problematic issue, both for your plants and fish. Having an aquarium can be really fun and rewarding too, but not when you have an invader taking over the space. Let’s not waste any more time and get right to it. We want to talk about what red algae is, how you can identify it, what causes is, how to prevent it, and how to remove it too. Get ready to say goodbye to that nuisance called red algae. We’re about to destroy it!

What Is Red Algae?

Red algae is also known as Rhodophyta which in ancient Greek roughly translates to “red rose”. There are actually over 3000 different types of red algae, most of which are multicellular organisms and grow only in saltwater. Only 5% of red algae species grows in fresh water hence why our focus here today is on saltwater tanks.

The algae is actually red in color because it has a pigment called phycoerythin, which absorbs blue light and reflects red light. Red algae usually grows in a leaf like or feathery structure, kind of like a bush with many little frills and soft points.

The funny thing is that red algae is not actually that harmful. Well, it can be harmful in some cases, but it does also have some beneficial properties as well. However, for the most part, aquarium enthusiasts do not want this invader in the tank, as the problems it causes usually end up outweighing the benefits in the long run. So, just to humor all of the naysayers out there, let’s quickly go over some of the advantages of having red algae in your saltwater fish tank.

Advantages Of Red Algae In Your Saltwater Fish Tank

  • Some fish do actually like to eat this type of algae, even as a primary food source. The red algae can absorb excess nutrients from the water, nutrients which your fish may be able to thrive off of once eaten.

  • Since red algae absorbs other nutrients in the water, it can actually help to slow down the growth of other types of algae. Now, this may seem like kind of a useless feature, exchanging one type of algae for another, but red algae is a lot less harmful than some other types of algae can be.

  • Red algae is awesome for sustaining a coral reef as they contain many nutrients which coral reefs need to grow and thrive.

  • Red algae does a fantastic job at absorbing excess nutrients, chemicals, and unwanted pollutants that may harm your fish.

Why Is Red Algae Bad For Your Saltwater Aquarium?

There are actually a few different reasons why red algae ends up harming your aquarium more than it benefits it. Here are some of the main reasons why you might want to remove red algae from your saltwater fish tank.

  • Red algae absorbs so much nutrients in the water that it may kill other plants. The lack of nutrients in the water due to red algae will leave your other plants hungry and with a lack of nourishment, thus causing them to shrivel and die. Red algae can also grow over plants, thus suffocating them and blocking their access to the light which they need to survive.

  • It just doesn’t look nice. Red algae, while some people may think that it looks okay, most would agree that having various plants, decorations, and the sides of an aquarium covered in it just does not look good.

  • As far as algae goes, in terms of growth, red algae is a total powerhouse. Just one little red algae cell can multiply infinitely. So, even if you scrub everything down, a single cell can cause a whole new outbreak. In other words, this stuff is ridiculously hard to get rid of. Once you have it, chances of eliminating it completely are very slim, which is actually why most people do not want to see it in their saltwater aquariums at all.

Why Is Red Algae Growing In My Fish Tank?

There are a few different ways in which red algae can make its way into your saltwater aquarium.

  1. Algae are very small multicellular organisms, so chances are that they might be hitching a ride on plants or fish which you buy from the pet store. Remember, these cells are small so you may not be able to see them at all. If you live in a place where red algae is prominent, there is a good chance that it is going to find its way onto a fish or plant which you buy.

  2. The soil that is beneath the substrate often contains all of the right nutrients which red algae needs to grow. Now, red algae may not necessarily be present in that soil, but if there is even one cell, the soil will definitely help it grow.

  3. Another thing that can cause the growth of red algae in your saltwater tank is when the levels of light are too low. Red algae thrives in darker conditions that lack sunlight, so if your aquarium does not have sufficient lighting, it is just asking for red algae to grow.

We have covered a really detailed guide which covers the A-Z on saltwater aquariums for beginners which you can find here.

Ways To Control & Get Rid Of Red Algae

Luckily for you, there are several ways in which you can prevent red algae from entering your saltwater tank. Just as lucky is the fact that there are also a few ways of getting rid of it once it has been spotted in your aquarium. Let’s go over all of these different control methods and how to get rid of red algae in saltwater tanks.

  1. One of the things that you can do to prevent red algae from growing in your saltwater tank is to pre-treat the plants you put into it. Since most of the red algae in your aquarium will most likely come from plants, this is most often considered to be the most effective preventative measure.

  2. Mix a bleach and water solution of 1 part bleach and 19 parts water and wash your plants off with it. You need to get this ratio just right. Too little bleach and the red algae won’t die, and too much bleach and you will kill the plants along with the red algae. This may slightly damage the leaves of your plants, but they should grow back fast enough.

  3. There are many fish out there which love to feast on red algae. So, if you want to get rid of red algae, or at least control its growth and multiplication, you can always introduce some red algae eating fish. (some shrimp also do).

  4. Another thing that you can do to eliminate or control the growth of red algae is to increase the level of lighting that is in your saltwater aquarium. Since red algae thrives in low light conditions, increasing the lighting is usually an effective control method. The problem with this method is that too much light can actually make other species of algae flourish more. The trick is to have enough light to get rid of red algae, but not so much as to cause other algae to grow.

  5. Another way of killing off red algae that has been proven to be fairly effective is adding more plants to the mix. Having more plants in the tank means that there are more things in the water absorbing nutrients. The more plants you have in the tank, the more nutrients they will absorb, thus eliminating the source of food which the red algae needs.

  6. Some people choose to resort to a copper cleanse. Now, this should only be a last resort, because things can easily go wrong. Yes, copper will kill the red algae, but do it wrong and it may also kill the other plants and your fish along with them. You can use copper sulfate to do this, but you will need to get a test kit to monitor the levels. Make sure to take out the fish when doing this, and only reintroduce them when the levels are sufficiently low as to not harm them.


Just remember not to panic if you see a little bit of red algae in your aquarium. The bottom line is that while this stuff can be a nuisance, there are indeed other more harmful forms of algae out there than red algae. Just follow the above steps in order to prevent and control algae growth, and you really should not have any problems. We have also covered a guide on finding the right salt mix here.