I don't think the couple SMB died due to too warm of water temperatures. Although as mentioned, very warm water does not absorb / hold as much DO as cooler water. In my experience they can easily tolerate 90F water if adequate DO and good water quality are present. The younger SMB 1-4yr olds tolerate warmer waters better than the oldest SMB. I assune the genetic stock came from somewhere in the midwest rather than far northern areas of upper US or Canada. A far northern strain of SMB may be more intollerant of warmest water temps. I agree with some of the others and think it might, repeat might, be a DO problem or some other problem.
I am not concerned with the GSH oriented with heads pointed inward around the aeration upwelling. This is common behavior for especially shiners. They are feeding on the zooplankton that is intrained in the upwelling water. Often predators will also hang out near the boil to prey on shiners or small fish feeding on the zooplankton in the water as it spreads across the surface layer.
Running your aerator as much as you are doing (24/7) should not result in low DO. Although pockets of low DO could be present depending on the placement of diffusers, bottom contours / shape, or maybe an island is present.
It is possible you have some ill fish. Bacterial and virus infections do occur in certain fish to cause death.
