How To Prevent and Remove Red Slime Algae (Cyanobacteria) From Your Reef Aquarium

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A Brief History

Anyone who owns a reef aquarium in 2019 or 2020 should know that Red Slime Algae or Cyanobacteria is not a part of the algae family, but it is a bacteria. It is one of the most annoying and resilient pests in your Reef Aquarium and can also harm certain types of corals. These bacteria do not necessarily appear to be red, they could be green, purple or black. Whichever color they may appear, they will surely sully what is supposedly an immaculate image of your tank. High levels of waste, phosphate, nitrate give them their necessary nutrients to thrive. If you leave them untreated in their inchoate stages, there is a chance that a complete overhaul of your tank will be necessary and that would just be a lot of work for you.

Digging Deeper: How can I prevent Cyanobacteria?

As I mentioned, Cyano thrives on increased levels of waste.  Here are some ways to prevent these bacteria to invade your reef tank:

Improve water circulation

If you see small patches of cyano in the corners of the tank and on the corner and crannies of your rocks, there is a possibility that you have poor water circulation. The water stagnates in those areas and they become breeding grounds for these bacteria. Check if you have the right size motor to for your pump or you can try to move things around to achieve better circulation.

Mitigate Nitrates and Phosphate accumulation

Nitrate levels should be maintained well with levels at under 10ppm and Phosphates should be at or below 0.05ppm. As  sko1971 from say that one of the leading causes is increased levels of Nitrates and Phosphates, thus it is important to maintain these levels at all times. This is because you may have low levels of Phosphate but still experiencing Cyano growth.

Provide better lighting

Get lights that are made for tanks only and change them regularly. Corals require lights that have wavelengths between 400-700 nanometers, which unfortunately the bacteria also get their photosynthesis at such levels. It is also important to change the lights regularly, I recommend under a year, because even if the bulb still works the spectrum of light it emits will not be good for the tank.  

Regular tank maintenance

This maintenance is not only to keep algae at bay, but it also helps to keep your corals healthy. Keep your filtration tight and don’t skimp on water changes. Remember that Cyano thrives on wastes so do not give them the conditions they want.

Removing Cyanobacteria

If you are already invaded by these pests then you are going to need a more direct approach in eliminating them. Here are some ways to remove Cyanobacteria from your reef tank:

Reduce lighting time

You can reduce the time of running your lights to not more than 8 hours. Bacterias need light to grow so keep them in the dark for a time to dampen their growth.

Use protein skimmers

Saltwater aquariums have algae because of disintegrated organic particles. Protein skimmers will help you get rid of these compounds and abate algae germination.

Phosphate reactor

This device can be helpful as some rocks or items in your tank increases the phosphate levels in the water.

Increase water circulation

Eliminate stagnated parts in your tank by increasing motor power. Doing so will eliminate spots where the Cyano breeds.


You can use chemicals to eliminate these bacteria, but do so with due diligence as some bacteria are important to maintain nitrate levels.

Reef Tanks and the corals give an innate feeling of relaxation. It is meant to be clean and pristine, but without the proper maintenance, just like any other garden, they will be overrun by pests. Keep them clean and you can a tank that you can be proud of.

Question for students (and subscribers): Have you ever owned a reef aquarium?  Please let us know in the comments section below this article.

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Historical Evidence

For more information, please see…

Skomal, Gregory.  Saltwater Aquariums For Dummies.  For Dummies, 2007.

The featured image in this article, a photograph by Egor Kamelev, is licensed under the Pexels License.


About Author

Abdul Alhazred

“But I don’t want to go among mad people," Alice remarked. "Oh, you can’t help that," said the Cat: "we’re all mad here. I’m mad. You’re mad." "How do you know I’m mad?" said Alice. "You must be," said the Cat, "or you wouldn’t have come here.” ― Lewis Carroll, Alice in Wonderland