This is exactly how my set up crashed & crashed hard three years ago, I still don't have a chiller but it is going to happen asap with the revamped set-up I working on.
Heat has always been my nemisis. It has killed I estimate about $400-$600 worth os corals & fish over the years. Here's what I know:
-spend the $$$ on a chiller, look at the cost of the live stock I've lost, could have easily bought a new chiller for that.
-in the meantime, A/C has kept me out of the frying pan (barely), my tank still creeps up to the bottom of the deathzone in heat like this, the only snails that can survive in my tank right now are Turbos.
-fans across the surface of your tank, lighting fixtures & sump do help.
-reduce your photoperiod to absolute minimum, or reverse it completly, or both!
-I have had little to no sucess in floating anything smaller than a 2L pop bottle of frozen H2O in my sump. You'll need several of these to have any hope, and that's for a small set-up. This really is futile in my experience. Works only if your really prepared and able to wwatch your tank closely & constantly.
-take all covers off the tank & sump to encourage evaporation.
-ensure steady top-up H20, bigger volume fights the heat better.
I am determined that my new set-up is not going to go through this crap, it has decimated my tank for years. I will be off to J&L's for a chiller very soon.
Hope this helped.
