29-01-2020, 20:48
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A clean aquarium where all its inhabitants feel comfortable is the pride of every aquarist, whether professional or amateur. But suddenly red algae appear in the aquarium. How dangerous it is and whether you can get rid of it quickly.

Let us see what it really is red algae, what dangers they pose to the inhabitants of the aquarium and how to get rid of them forever.

What is red algae?

It may sound strange, but red algae are not algae at all. It is actually a species of bacteria known as red algae cyanobacteria.

Cynobacteria represent one of the oldest forms of life, dating back at least 3.5 billion years. Although cyanobacteria literally mean blue-green bacteria', only about half of these bacteria are actually blue-green in colour. Most of the cyanobacteria found in saltwater can vary in colour from dark green to orange-yellow, copper, dark purple and even black.

If you notice red slime patches in the aquarium, you should immediately take measures to remove them. This aggressive algae will infest the entire saltwater aquarium very quickly.

Red algae

The dangers of red slime

Although red algae can make an entire aquarium look unattractive in a short time, it is harmless for the fish.

So what is the real problem with red algae in your saltwater aquarium?

Causes of red slime algae

  • Lighting fixtures

The most common source of unwanted cyanobacteria growth is incorrect or inadequate lighting.

Most species of algae, and particularly red slime algae, thrive in the emitted frequency spectrum between 640 and 680. Unfortunately, most corals require light in the 400 - 700 nm range, which poses an additional problem for red algae control.

  • Irregular maintenance

Irregular maintenance of the aquarium in general leads to a number of problems and red algae is often less of a concern in this case. Some aquarists change the water in the aquarium irregularly, which may lead to an accumulation of organic matter which is a fertile medium for the growth of various algae.

  • Lack of water circulation

If you notice that cyanobacteria are only growing in certain areas of your aquarium, it is often the case that the water is not circulated. An overabundance of nutrients in these areas leads to a rapid growth of red algae.

  • Water aeration is not carried out.

Fish and any plants in the aquarium breathe oxygen in the same way as we do. Red slime algae thrive in non-oxygenated environments, which is why it is important to aerate the water.

  • Chemically unbalanced water

Filling the aquarium with water containing too much nitrate or phosphate may result in the rapid growth of cyanobacteria in the future. The concentration of phosphate may be higher, as it is one of the end by-products of the nitrogen cycle. Thus, they may reach unsafe levels if the aquarium is not maintained for a long time.

How to prevent red cyanobacteria

  • Regular water changes

Regular water changes are very important to keep all water parameters at an appropriate level. Regular water changes will reduce the concentration of organic matter in the water, which promotes the growth of algae.

  • Maintain high PH levels

Make sure that you maintain proper pH levels for your fish species. As a rule of thumb, pH levels should be between 8.1 and 8.4. High pH levels inhibit the proliferation of red algae.
Reduce phosphate levels

Clean your filters as often as possible. If you find elevated phosphate levels in the aquarium, rinse or replace the filter media.

  • Clean the substrate

In addition to regular water changes, you should also clean the substrate regularly. Use a siphon to remove any remaining organic waste and uneaten food.

  • Do not overfeed the fish

Give the fish as much food as they can eat in a few minutes. If the fish do not eat any more, remove the food from the bottom ground, as decomposing food causes algae growth.

Red algae


Red algae can be annoying pests, but they are ultimately harmless for the fish in your aquarium.

Now that you know how to get rid of cyanobacteria and how to prevent its re-growth, hopefully your aquarium will be as clean and healthy as possible.

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