I've been getting pretty high temps lately too... been 90+ the last few days. I find that freezing water in ziplock (or 2-litre bottles) is a good way to keep the temp from getting any higher. I also turn the lights off an hour or so earlier than normal, and open up the canopy to let the warm air escape (I run a fan over the top of the water at night to help dispurse the warmth).
Good luck. If you find a better, easier, cheap way, let us know!