No one wants their beautiful reef tanks to be filled with filthy red slimy algae. These algae are not only irritating but also hard to get rid of. Most beginner reef tank owners face this problem once in a while and get frightened about what to do with them.

One thing is for sure, you don’t have to get frightened. These algae might look toxic, but they usually do no harm to your fish. So, if your tank is attacked by a bunch of red slimes, be patient and take the necessary steps.

In this article, I am going to talk about how to get rid of red slime algae in reef tank and what to do to prevent them.

What Are Red Slime Algae?

Though the name is algae, Red Slime is actually a type of bacteria called “cyanobacteria” with a red pigment. They are extremely slimy and grow in sheets. Generally, they can be seen on a small portion of the aquarium but they produce really fast and you can find them covering the entire tank pretty soon.

Though the red slimes in the aquarium are not toxic, they can be quite irritating and at worst cover your whole tank. So, you might want to know about all the possible ways of getting rid of them.

Why Your Tanks Gets Attacked by Red Slime Algae?

You need to know the real reasons behind these algae attacks before trying to get rid of them properly:


Inappropriate lighting can be the most common reason for an algae outbreak. While lighting is necessary for some living things in your tank like corals, it can also cause the algae to grow fast.

Unfortunately, the algae need a lighting between 640-680 nanometers, whereas the corals need 400-700 nanometers to live. This certainly brings forth a problem.

Too many nutrients:


Dirty water, dead fish, or badly preserved live rock can increase the number of nutrients in the water resulting in algae growth. So, in this case, getting rid of the nutrients will help you to kill the red slimes.

Not Enough Maintenance:

Not maintaining the tank properly can lead you to a lot of problems including the algae attack. Also, you will have to change the water often to keep a balance in your aquarium.

How To Get Rid Of Red Slime Algae In Reef Tank

How to Get Rid of Red Slime Algae?

Red slime algae can attack your tank for different reasons and to get rid of them you will have to first figure out what’s causing them to grow fast. After you have done that, there are a number of ways you can get rid of those annoying bacteria:

1. Controlling Organic Compounds

Algae are known to feed on organic compounds like nitrate and phosphate. Phosphates usually do not have any impact on your fish’s health.  So, you can easily control the algae by dropping your phosphate levels. You can use Phosphate Remover to lower your phosphate level in the reef tank.

You should know that a high level of nitrate is very harmful to your fish, not to mention the algae growth. Changing the water frequently will keep your tank’s nitrate level normal.

2. Reduce lighting

These algae rely on photosynthesis for their living. So, using anything other than bulbs on the aquarium can result in Algae outbreaks. Also, you shouldn’t use the light more than 7-9 hours a day to avoid sudden red slime growth.

Additionally, you can try keeping the lights off for 3-4 days straight. Having blackouts for a long time can help you to get rid of the cyanobacteria all at once.

3. Stop Hypersalinity

Hypersalinity occurs when you get your evaporation with saltwater. During the evaporation, salinity increases due to the salt molecules remaining behind. And most importantly, Hypersalinity causes the red slime algae to grow in large.

You can stop that by topping off with fresh water instead of salty water. You can also check your water’s salinity level a few times a week with a refractometer.

4. Increase the Water Flow

Algae are quite common in places where the water flow is rather weak. So, increasing the water flow might cause them to die eventually.

You can use different types of powerheads or wave makers to increase water flow.

5. Clean the tank regularly

Cleaning the tank on a regular basis will surely help you to get rid of the slimes. But this process can take time and you might have to clean your tank much often than you normally do.

Also, if you are using any live rocks, make sure they are preserved properly. Otherwise, they can cause the algae to grow too.

6. Chemicals

Using chemicals is the fastest way to deal with Red Slime algae if applied carefully. You need to calculate the right dose considering your tank volume. Also please be careful about using algaecides and erythromycin in the tank as it will do more harm than good. You need something that doesn’t have these and perfectly safe for your corals, fish and invertebrates.

How to Prevent Red Slime Algae?

The best way to keep the red slimes away is by cleaning your reef tank and changing the water regularly. Also, you should maintain a safe level of phosphate and nitrate in the water.

Make sure to use a limited amount of lighting in the tank and avoid spreading antibiotics. If you can maintain these small things, your tank should be good to go.


So, this is how to get rid of red slime algae in reef tank. Red slimes can be a little difficult to get completely rid of. But if you try to take the steps mentioned above you will see the results pretty soon.

The best thing is to keep them away rather than trying to get rid of them. Keeping your reef tank clean is the finest way of keeping all kinds of problems away. Also, make sure to maintain an appropriate light in your aquarium so that the algae can’t grow but the corals can live peacefully.

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