How to fight cyanobacteria in reef tanks

How to fight cyanobacteria in reef tanks

They are a plague in reef tanks and everyone who practises this hobby will sooner or later come into contact with them: we are talking about cyanobacteria. But don't worry - if you take early action and follow our tips, you will get rid of this plague quickly.


Cyanobacteria form red or green mat-like coatings, which can completely cover both the substrate and the stone structures in your aquarium if they are very heavily infested. They do not even stop at corals and other sessile organisms. But it does not have to come to this point. If you act early, you will soon get the problem under control again.
We will give you five tips on how to eliminate the unattractive cyano layers:

#1 Vacuum the cyano films regularly

If cyanobacteria have already spread in your aquarium, you should try to suck off the reddish coatings repeatedly. The resulting 'waste water' must be disposed of! In order not to lose too much water in the tank, use a thin hose. It can take a while before the regular vacuuming of the coverings shows an effect. Here it is important to keep calm and vacuum, vacuum and vacuum again!

 how to fight cyanobacteria

There is no need to panic when spotting cyanobacteria. In most cases, some vacuum cleaning and a portion of good bacteria will already help to solve the problem.

#2 Bacteria against cyanos

Cyanobacteria are particularly common in aquariums that are biologically unstable. In this context, biologically unstable means that there is no functioning bacteria community (yet). Many "good" bacteria in your aquarium compete with the cyanobacteria and thus restrict their development. The use of living rock or special bacterial solutions such as Nitribiotic are beneficial in this respect. The addition of bacterial solutions is particularly effective if you introduce them directly into the substrate with a syringe.

#3 Phytoplankton against cyanobacteria

Similar to the use of bacteria, phytoplankton can also compete with cyanos and limit the spread of the plaque. Living phytoplankton of the genus Synechococcus sp. (itself a cyanobacterium, by the way, but which does not form deposits and is "good" for tank biology) has proven to be particularly effective.

#4 Avoid dirty corners

Cyanobacteria love dirty areas and therefore prefer to occur in places where a lot of debris is deposited due to a too weak or missing current. It can already help to improve the flow pattern in your tank. Try to realign your pumps or increase their performance a little. If this is not possible, you can think about using additional pumps or exchanging them for stronger ones. Furthermore, you should clean the substrate in your aquarium from debris at regular intervals.

 what to do with cyanobacteria

Dirty corners, low flow areas and dead pieces of coral are typical regions to find cyanobacteria. Pay particular attention to those and you will have a chance to react early.

#5 Check and optimize your water parameters

A wide variety of parameters can promote the growth of cyanobacteria. Some cyanobacteria benefit when no nutrients are detectable in the water. Still other species have the ability to absorb molecular nitrogen from the environment and fix it in the form of ammonium. In case of a nitrogen deficiency and a simultaneous phosphate surplus, such cyanobacteria get a real advantage. Therefore, make sure that the nitrate:phosphate ratio is balanced (ideally 1:100) and, if necessary, raise the nutrients slightly above the detection limit. Increased phosphate concentrations can be reduced by using a phosphate adsorber.

#6 Supporting measures

If possible, avoid carbon dosage (e.g. vodka method, products with ethanol or sugars as ingredients) while the cyano problem exists, as these generally promote bacterial growth (including cyanobacteria). Furthermore, you should temporarily stop adding trace elements and amino acids. An additional filtration with activated carbon can be useful to remove possible toxins of the cyanobacteria. Also check your silicate content in the water and take measures (e.g. renew the mixed bed resin of the osmosis plant) to remove silicate.

#7 The last resort

If you have taken all the measures listed here, but have not seen any improvement even after several weeks, you can consider using an anticyano preparation. The trade offers you numerous options here. However, you should make sure that the preparation does not contain any antibiotics. As the tank biology is often severely affected by the use of these preparations, they should be considered as a last option. If you do decide to use them, it is recommended that you stabilise your tank biology after the treatment by adding a bacterial solution.

We hope that these tips will help you get rid of your cyanobacteria and that you will soon be able to enjoy your aquarium to the full (cyano-free) extent again. The most important thing is: react early and keep up!