There are multiple factors that can cause bacteria/algae to bloom in your reservoir -- lack of aeration is one of them. Heat is another. Aeration alone will not prevent 100% of the potential issues in hydro. Letting a reservoir get into the 80s is just asking for problems and is overall bad advice.
Well, if I were to have been able to give this advice to myself years ago, it sure wouldn't have been bad! I never got any type of root rot or damage doing that for multiple years, and instead of running a chiller, I was able to use that same power to run another light. My setup may have been unique in that I was running a pond/septic/fishery style aeration setup, not airstones with the little air pumps most people seem to use. It made my 45 or 60 gal dwc tubs look like water at a low boil. That is the biggest reason I switched to that setup vs my sprayer system in tubes. I can't remember the cycle time, (maybe 2 off 1 min on?) but I found that the 68 degree recommendation was not sufficient for that, likely due to the pooled water warming in the tubes on the off cycle. 62 degrees woke the plants right up. But with the knowledge I have now, I'd bet adding airstones inside the tubes would have accomplished the same thing. As I'm sure you, and most people in hydroponics know, water's ability to hold oxygen is inversely proportional to temp, but what a lot of people don't also seem to consider is with bubbles coming up through the water, it doesn't matter if the water can "hold" that oxygen at all, as long as it comes in contact with the roots.
I always wondered how high I could actually run that system without damage. Higher grow room temp is higher plant metabolism, but also higher transpiration, etc. I was running a co2 burner. Typically the room was in the low 80s, but in the summer it frequently could get higher.
