+2 to both posts above. Invasive algaes that over grow and choke out corals are a definite no go. Those that look nice and help with nitrate issues are fine. I've got a nice looking small red algae that I let go in one of my tanks, and it now covers all the powerheads, much of the LR
, and I have to manually remove it to keep it from overgrowing the corals. On the other hand, I have a nice large red algae in another tank (had it there for years), it sits backhind the LR
in limited light and other than growing slowly has never caused any issues.