Good morning! We have an IBC that we're going to use for our fish, but the water in it is currently in the high 80s/low 90s. I'm afraid to put the fish in there, especially when we have another heat wave like earlier this week. How are you guys keeping your fish cool? We have about 50 bluegill currently residing in a fishtank indoors . . .
You might want to build a plywood enclosure for your tank with a plywood lid. It will preserve the plastic from the sun's damaging rays and keep it cooler.
I've been using bluegill in my systems in Sac for the last few years and high temperature has not been a problem. I shade the tanks as much as possible. Bluegill should be fine up to 90 degrees, with average growth up to 85 degrees and optimum 80 degrees (per "Aquaponic Food Production", Rebecca Nelson). They might tolerate occasional temps higher than 90 too. Also, it's my understanding that temperature stability is important. That is, fish should tolerate fairly extreme temperatures more easily if the temp doesn't fluctuate wildly. They are more likely to have problems with big temperature swings, which is why you'll sometimes see more fish deaths in spring or fall when temperatures are more volatile. In fact, the only time I had a problem with my bluegill was during a big temp swing in spring one year, combined with plumbing failure.
As you probably know, warmer water holds less oxygen. So it's good to build splashing into your system wherever possible and plenty of air bubbling through especially when it's warm. And keeping your fish density low helps.
I like all of Tom & Richard's suggestions except for building a chiller. Cooling water electrically is very energy inten$ive. On the other hand, theoretically you could use a reconfigure a solar water heater to act as a chiller, radiating heat to the air rather than gathering heat from the sun, but I'm not sure it's worth the trouble.