What is a Cyanobacteria bloom and how do I get rid of it?

An unholy alliance of bacteria and algae, Cyanobacteria or Blue-green algae are adaptable, tenacious, and ugly. Their partnership allows them to thrive on light or nitrogenous waste and there’s often plenty of both in our home aquaria.

Because they’re so unpalatable, algae eaters that tackle these kinds of nuisance growths are rare but Short-finned mollies (Poecilia sphenops) are an excellent solution if compatibility allows. Their adaptability makes them suitable for a wide range of conditions, unlike their Sailfin relatives which need either salt or high KH to thrive. Substrate sifting creatures can be useful for eliminating dead spots and pockets of waste but make sure that you don’t expect them to eat the toxic slime and reward them for their labours with a suitable diet.

Removing the nutrients that help them to thrive is a big part of beating this menace and chemicals can be useful in breaking the cycle of recovery. Reducing the levels of organic waste and increasing water flow and aeration can play a big part in control. Siphoning the algae out and using a gravel cleaner can be a good way of starving it out and resin filter media that remove phosphate can give a useful shortcut, especially if your tap water is high in nutrients before it is even added to the aquarium. As light is crucial to their growth, blacking out the tank for a few days can be a useful way to take back control.

In marine aquaria, it can be a sign to increase water movement and reduce background organics. A regularly serviced protein skimmer with a small ozoniser can be a very efficient way to shift things in your favour.