3 of my tanks are running the Penn-Plax Cascade 700 and 1000 series canister filter/pumps with the spray-bars that go almost the full length of the tanks. 29g, 40g and 55g.
All 3 have this.... funk.... building up on them. looks kinda like algae and I've considered wiping it off during the next water change. Is that alright? OR, is that actually beneficial bacteria
growing up there and I need to leave it alone?