I believe that this IS algae (as opposed to cyanobacteria, which is commonly referred to as Blue-green algae), and I know that it takes advantage of nitrates in the water. The best way to avoid it is really to get an algae-eating fish. These guys scarcely add to the bioload. I agree with Krap that you can probably afford to get one or two otos or a small pleco.
If you are really opposed to this idea, two options exist:
1) Do frequent water changes. If you change the water a couple of times a week the algae will have less nitrate to feed on.
2) Probably a better idea, get some low-light, fast-growing plants. Hygro (Hygrophila polysperma), Java Moss, Hornwort, Anacharis all count. These will outcompete the algae for the nitrates. However, if your tank contains aggressive fish, the plants may be "outcompeted" by the fish and become food. If you're housing cichlids, and possibly gouramis, this might work less well.