rhodophyta

I have two "algae" problems. One is a black slimey algae that I can eradicate if I treat a planted tank with a half-dose of erythromycin, but it soon comes back. I suspect it is some kind of cyanobacteria. Over years of fish keeping I have gotten sensitive to the cyanobcteria and have an allergic reaction if I put my hands in a tank with it.

The other is a very slow growing red algae, almost like the pink to red calcareous algae in saltwater, but this is bright red, and when it gets on the glass, it amost seems to grow inside the glass rather than on the surface, so all a razor blade does is make it a brighter red. It is not affected by even a full dose of eythromycin.

trenac

The first sounds like BGA, just in black form. The usually cause is low nitrates. Also try increase water flow. Just keep it removed manually & get your water chemistry balanced.

The second could be green dust algea, which is not always completly green. However it does scrape off easily. However I have found that the red takes a little more effort to get off the glass. Again make sure that you are keeping balanced tank:ferts, C02, lighting & maintenance.

rhodophyta

Actually, I put an FX5 canister filter on the 150, hoping it would eliminate the black slime with the increased current, but it hasn't. I have an allergic reaction to it, so manually removing it, more than what I can siphon out, is not an option. There is increased current though. Any plant that gets knocked out of the substrate ends up in one eddy opposite the filter.

The red algae seems to be grounded in the pores of the glass. Most of it is below the level of the razor blade. It is completely red, no green, and it does not form a sheet like the green dust algae. Spots of it that are several years old are still no bigger than a dime. Newer spots grow to that size, and then seem to be stopped and new ones start.