My brother and I used to put ice in Ziploc bags and float them in the tank. I always wanted to try a kegerator approach where my return line went through a bucket of water inside or the fridge before going back to the tank so I could keep natives up here.
That's a cool idea! (groan)lol
IMO, as long as the fish aren't showing signs of stress, why bother? But if you want to keep cold fish, then I guess you would have to do something. Even something like the fridge idea isn't viable for everyone. I wouldn't want yet another appliance in my basement contributing to the heat in the house, though I suppose if your tank was already in close proximity to a fridge.... then why not?
Although I bet most cold water fish are tough enough to endure the high temps with no issues... they tend to be hardier fish I think. I see fish all the time in dwindling river overflows in the summer when animals are feasting on the trapped fish. The water has to be in the high 90's based on what I'm reading in my house... and all of those fish are still alive.. catfish, carp, crappie, ect.