Reef woes

[Bree]

We are novice "reefers", having had our 110 gallon tank for about 9 months. From the beginning we had great luck with any corals we introduced into our tank, but no luck with fish. Lately, our corals started looking pale and withered when we noticed our temperature had increased from our usual 78 degrees to 84 degrees. We adjusted our temperature, but are wondering if our sad corals could be attributed to this...maybe our fish fatalities as well?
We recently had a blue tang and 2 green cromuses (sp?) die, in the past have lost 4 or 5 clowns, as well as a butterfly fish. Our water quality always checks out perfect.
Any suggestions at all would be appreciated.