Algae

[fish_frenzy]

Blue-green algae (cyano bacteria) is toxic to some fish. It will kill your plecos/ottos etc. I learned the hard way. It is actually not an algae, but a group of bacteria capable of photosynthesis. It usually appears in tanks that are overfed or need more water changes, but can occasionally appear in mature, stable tanks. Hope this helps.

Tammy