my ph doesnt just fall it just stays around 7.8 I can get it up to 8.2 but then it falls back down overnight. It is a 75 gal, ls, 80 lbs lr, yellow tang, hippo, lionfish, puffer, blennies, dwarf angle, clown,4 crabs, urchin,2 star fish, 2 oysters, and a couple of things that came off my lr...