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Written By: Sirdarksol for the FishLore Magazine
An Aquarist's Guide to Blue-Green "Algae"
Your tank is running well, except for a light dusting of an intense green algae on parts of the
glass. All of the sudden, sheets of bluish-green stuff are spreading across the decor. Still, it's just
an algae outbreak. Easily dealt with. You step up your water changes and manually remove the
algae. Day after day, however, it comes back. You buy a cleaning crew of shrimp, snails, and/or
fish known to eat algae, and yet nothing seems to change. Worse, you think your fish are
getting sluggish. You check the fish disease charts, and they don't seem to fit any of the profiles.
They sometimes hover near the top of the tank, at other times the bottom. They never seem to
gasp for breath, but always are languid. The more tender inhabitants may even be dying
without apparent reason. You bring out the big guns. You go out and buy a bottle of algaecide.
And still, nothing happens, other than the death of any inverts and live plants that happen to
live in the tank.
This is not an uncommon occurrence, nor are these actions unreasonable, given the
information that most aquarists have. For all intents and purposes, this seems to be some sort
of algae outbreak. Even its name, "blue-green algae" says so. However, it isn't an algae. It's
actually a strain of bacteria known as cyanobacteria (its name derived from its vivid color, which
would be beautiful if it didn't signal so much trouble for an aquarium). In addition to blue-
green, cyanobacteria can be black or even red. Freshwater Aquarium e-Book