Please DO NOT use pH Down either, no matter what the employee at the fish store says (My prediction is he'll recommend it like mine did)! 8.0 is absolutely fine for all the fish you have as long as they are properly acclimated to it. It is MUCH worse to have a large fluctuation in pH, it just needs to be consistent. And pH down won't work -- it will swing the pH down significantly pretty quickly (severely stressing and possibly killing your fish) but within a few hours I guarantee it will swing back up to about 8.0 (again stressing the fish). And if you add more, the same thing will happen again. The reason is buffer chemicals in water with high pH will naturally buffer the pH back up to its natural level. I don't know the scientific explanation well though, sorry, I'm sure someone knows more than I. But, I know I tried this myself when I first started, it was a disaster.