Can someone tell me if this is GHA? I believe it is and have a fair bit on my rocks. Tank is 1.5yr old 60g brought second hand with the rock, phos and nitrates are zero. I plan on removing the rocks tomorrow during a water change to try and remove it and scrub it off. I don’t want to use any chemicals at all, I have lots of various snails I believe some turbos, astraea and Nass and 6 fish including a lawnmower.