What Steps Should I Take To Remove Cyanobacteria From My Fish Tank?

Did you adjust the lighting to eliminate the energy source for cyanobacteria?

Did you reduce the feeding of your fish to eliminate the food sources for cyanobacteria?

Did you remove large clumps of bacteria by hand with a small net?

Did you aerate the aquarium?

Cyanobacteria are photosynthetic. However, they use wavelengths of light that are not used by higher-order plants. Reducing or eliminating the wavelengths that they use will drastically reduce their ability to feed and propagate. Replacing the bulbs in your aquarium with balanced light bulbs (6,400K to 14,000K) or actinic 50,000K bulbs will immediately reduce the amount of useable light for the cyanobacteria.

The primary food source for Cyanobacteria are phosphate (PO4) and nitrate (NO3). These usually come from fish food leftovers caused by overfeeding. To eliminate the dissolved organic compounds, the first step is to complete a 30 percent water change. Follow this with a significantly reduced feeding schedule. Feed your tank about one-third of the normal amount. Ten percent water changes can be done every other day for the remainder of the week to bring the amount of PO4 and NO3 to acceptable levels. Once the tank environment is back to normal, feeding schedules should be adjusted to reduce the amount of waste food decay.

After the first day of new lighting and reduced nutrients, the bacterial blooms will begin to fall apart. Removing large clumps of bacteria by hand with a small net will significantly reduce the strain on the filtration system and prevent it from clogging. Remember to sterilize the net in a solution of 15–25 percent bleach when you are done so you don’t accidentally reintroduce Cyanobacteria to your tank at a later date.

Once the large clumps and sheets of Cyanobacteria have been removed, adding or increasing the amount of aeration in the tank is the next step. Cyanobacteria thrive in relatively still, poorly oxygenated water. Adding a bubbler or turning up the powerheads in a tank will remove stagnant areas from the tank and reduce the areas in which the bacteria can proliferate.

Lowering the temperature of the tank below 76 degrees Fahrenheit will also slow the growth of bacteria. This is only advisable if you are running a freshwater set-up as temperature changes in a marine environment can cause unnecessary stresses on the fish and corals in the environment.