Turn off any lights that are close to the tank. Even fluorescents will add heat. I assume that you do not have central air conditioning, since keeping the ambient room temperatures cooler is the best way to control heat inside the tank. I don't have this either, because it isn't usually needed in SE Idaho, but we do occasionally get hot days.
I put ice in the waterways, and blow a fan across wet terry cloth towels with crushed ice on top of the vented tank. (I raise the lids over those tanks that also have a screen and put the wet cloth over the openings.) It all helps a little. For upstairs, where it tends to rally get overly warm, I also purchased a room cooler--the fan/water vaporizing type. This doesn't help a heck of a lot. In So. Cal. you may have to purchase one of the window air conditioning units.
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Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
7 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
6 P. terribilis mint and organe
4 D. reticulatus
4 D. castaneoticus
2 D. azureus
4 P vittatus
2 P. lugubris