Nothing new to add here that hasn't already been said. My 60 gallon killed every fish I put in there and my tank parameters were the same as yours. In order, I lost a clown pair, a lemonpeel angel, a flame angel, another ocellaris clown, and finally a purple firefish. Then, after waiting a month or so, I tried a 4th clownfish and he made it, then a flameback angel, then a watchman goby, yada yada yada. Point is I did nothing different between my failures and successes.

Also, and this may not be the case, but try a fish from a different lfs. Sometimes, even a good store can get a bad batch of fish.