chill out guys...literally...
aquaskilz - kclewis is right, tank temps in the hottest of months should have been considered when planning your tank, not after its setup; he did give you sound advice, it may not be what you wanted to hear, but it was true nonetheless.
kclewis - your advice is correct, but dude, his tank is already setup, telling someone they shouldnt have a tank after they already hacve one isnt going to be well received by anyone, NY'er or not...maybe just change your delivery a bit.
aqua - you mentoned something in passing about not keeping an open system...most of our reef tanks are open, ie, no glass on the top. this is for a bunch of reasons, one of them being temp control...by having an open top, heat is allowed to escape your tank via evaporation...if you keep it closed, not only are you keeoping th heat in, but you are slowing down gas excvahnges...
if you have (had) jumpers, use the brs 1/4" mesh and window screen frames to make a top...
you dont have to run a chiller, but you will need to do a few things to keep temps under 90.
1 - keep windows open, move air with fans in the apartment
2 - open the tank up, and put fans across the top
3 - put fans across the sump surface
4 - keep those btotles of frozen RO handy
FWIW, during the summer my tank runs a little above 80 on the hottest days, and everything is fine, no issues. i put a fan across the sump and that kept temps under control. i just switched to LEDs so im hoping its better this year...