Im a big proponent on keeping your tanks in the recommended temperature levels of the fish you are keeping. If that means not being able to keep certain fish, so be it. I live in FL, so heat is a very big issue. It has been so hot here I'm not sure the AC has shut off in over a week. I keep 3 African Clawed Frogs, which, as some of you may know, are cold water amphibians. I have a cooling fan directed at the water for evaporative cooling 24/7 to keep the temp in the low 70's.
If your ambient temperature is in the 80's, then your tank likely is as well. There are very few fish that can tolerate these conditions for long periods of time. In fact, the die off could have happened, black out or not. Fish can adapt to temperatures a few degrees higher than their optimal habitat temperature, but it will significantly reduce their lifespan.
In short, both heat and cool your tanks.