An Introduction Blue green algae, or Cyanobacteria, are remarkable in as much as they are somewhat of a hybrid between algae and bacteria. In some ways they resemble green plants and algae, and in others they are much closer to bacteria. The latter explains why antibiotics are sometimes used to rid the tank blue-greens. Although this method results in their disappearance, at least for a while, the dangers associated with using them in an aquarium need to be stressed here.
Biological filters contain many bacteria themselves.
These, too, can be affected and more than likely will be. Note that since live rock and live sand contains bacteria as well, the use of antibiotics will affect them as well. Cyanobacteria are photosynthetic. They release oxygen and uptake carbon dioxide, depending on the photoperiod and lighting conditions. Cyanobacteria contain pigments.