I should get a test kit but some Yamato shrimp would also tell me if levels are too high. Thing is, I have little alga to speak of and no more BGA.
IME, lowering BOD, a skimmer and an oxidizer like chemiclen (when all else failed), kept BGA from reoccurring.
IMO, when the other bacteria are having trouble due to poor oxygen exchange, pH, temperature and/or a barrage of mulm, BGA steps in.
Might check any house filters, if you use one. I'm imbarised to say, I might not of always kept up with my filter changes in the past.
