High PH

[willwagner2k]

I'm a newbie that just encountered his first disaster. I have a 40gallon tank with a 20 gallon overflow, Live Rock, [acronym:3943b36c0e="Deep Sand Bed"]DSB[/acronym:3943b36c0e], a couple of small soft corals, and until recently, a clarkii clownfish and a kole tang, as well as some hermit crabs and snails. I've started using [acronym:3943b36c0e="Natural sea water"]NSW[/acronym:3943b36c0e] from a [acronym:3943b36c0e="Local Fish Store"]LFS[/acronym:3943b36c0e] for water changes (10% every two weeks) and have [acronym:3943b36c0e="Reverse osmosis"]RO[/acronym:3943b36c0e] water to replace lost water.

I've been testing my water routinely for Ammonia, Nitrites, and Nitrates regularly and they've all been non-existent. I also regularly check salinity 1.024-1.025 and temperature (81*).

The corals are doing well, no observable stress, but 4 days or so my clarkii died (didn't appear to have any ick or skin disorders), and then one of my hermit crabs, and this morning my tang. I really feel bad for not checking other parameters sooner, but it looks like my [acronym:3943b36c0e="Powerhead"]PH[/acronym:3943b36c0e] is high 8.6, althought my [acronym:3943b36c0e="Alkalinity"]Alk[/acronym:3943b36c0e]. is normal.

Was the high [acronym:3943b36c0e="Powerhead"]PH[/acronym:3943b36c0e] what caused those animals to die, or is it likely there is another culprit? I don't want to add more fish until I'm certain they'll be ok, and I'd be happy to wait 6-8 weeks (to allow any parasite to die) if that would help assure better success.

Also, if I wait some weeks before adding new fish, should I continue to add food to the tank so my [acronym:3943b36c0e="Deep Sand Bed"]DSB[/acronym:3943b36c0e] and inverts stay healty?

Thanks for your advice and counsel