bigfish93, if it is cyanobacteria, it is not harmful per say but it will kill plants via suffocation of the leaves, and it indicates very bad conditions which will eventually take their toll on the entire aquarium including the fish. Cyano is not an algae, it is a type of bacteria. I wrote on length about cyanobacteria yesterday, here is what I said copied over.
Cyanobacteria is always and solely an organics issue. Reducing light including blackouts, treating with antibiotics, removing it by hand--the cyano will (or may) dissipate but will always come back (as you've noticed) unless the cause (organics) is fixed. For one example, I just had a bout of this in my 70g. I hadn't really noticed it at first, until one day while feeding I saw that about half the Pygmy chain sword
were darker green, and looking closer I saw they were covered with cyano. It flashed across my mind that the canister filter on this tank had not been cleaned for about 6 months [won't get into all that]. I disconnected it, cleaned it, new pads...removed the cyano by hand during the water changes over the next two weeks (once weekly, no more)--end of cyano. For 3 weeks now, crystal clear. Organics is the cause, nothing else.
Insufficient water changes, overfeeding, overcrowding (fish) and all cause a buildup of organics. Waste in the substrate should be broken down by snails (Malaysian Livebearing will help here) and bacteria, but this has to be balanced with the needs of the system (plants use some of these, other types of bacteria use the nitrates). Weekly partial water changes of 40-50% of the tank volume should keep this balance. Fish do not need more than one feeding per day (except fry), and can mis a day or two a week with no harm, so going above this may contribute.
Never use antibiotics to deal with cyano. Yes, they work--after all, cyanobacteria is just what it is named, a bacteria, and we all know that antibiotics kill bacteria. But they kill other bacteria than the cyano, which can be just as dangerous. They can affect fish. And organisms do build up immunity to antibiotics as we all know ourselves. And they can kill some plants. Never use any antibiotic in an aquarium except specifically to target a bacteria that is harming the fish.
This was the other thread: Foamy Water & Cyanobacteria