Yeah, sounds like BBA (Black Brush Algae) which is actually a red algae. It prefers alkaline water and is hard to get rid of except with CO2
kept at 30ppm, in my experience. But you can slow it down with frequent water changes and thoroughly cleaning or pruning where it grows. There are some pretty good articles in the Krib (online) about dealing with BBA. But 30 ppm
was my silver bullet which Rex Grigg turned me onto. Good luck.
26 Gallon Planted Community, 90 Gallon Planted Community - Rena XP3, XP2 Filters, PressurizedCO2
, Eco or Flourite, TEK 4x54 T5 light, AH Supply PC