I've got the exact same issue at the moment. I have had it in the past, and skimmed by without a chiller, and I really cannot afford one at the moment.
Here is what I'm trying:
1) Turn the lights down. i turned off one bank of t5's completely (I have two banks of four) and left my hood cooling fans on at all time. The tank now sits next to a window with evening sun so I think it probably doesn't need as much artificial light anyway.
2) Took off my glass lids. Still have the canopy of course, and I'll have to deal with more evaporation.
3) Turned the heater down 3-4 degrees. I figure if i start the day at a lower temperature it won't get as hot later in the day. That's a balancing act, but I hope I can get it down to 78ish in the morning it won't go over 82 later in the day. It went down to 81.5 this morning, going to give it till tomorrow and see if it goes any lower.
If these are ineffective, I am going to put some blinds up in that window and close off the sun light, see if that solves it. Though the natural sunlight has really perked up my corals
After that, I'll probably buy a chiller whether I want to or not. I'd need 5-6 2 liter bottles to cool off my tank enough to matter, and I don't have that much freezer space.
