Several points:

I gave up on using feeding charts in my ponds early due to the difficulty of capturing fish for sample weights (many floated up dead from the stress a few days later of a quick catch and release) and the variation in growth of my fish.

I think your air temp cutoffs for you diffusers are too low IMHO. Granted your water temps can go up during the day in summer, but it as we all know from basic science it takes a lot of energy to change water temperature.

I turn of my diffuser about 8 or so in the morning and it goes back on at dusk regardless of the air temps.

You are right if you have an algae bloom and some aquatic weeds you are making oxygen during the day. However be aware that a week feric iron solution will mimic the color of an algae bloom. (greenish)

I think you have some colder water than you think. At 70 F. you should be seeing some mortality or morbidity from stress. But again some of your fish may never float to the surface and the ones that do may be carried off by scavengers while you're not there.

If I'm wrong more power to you though.

I'm also feeding only once a day now, and that is in the morning when oxygen levels are rising again after a night of decreasing D.O. levels due to repiration of phytoplankton. Had a very experienced trout farmer tell me to do this -- especially if my water temps are marginal, or my density is high.

I'm losing a few brook trout here and there but I think it's due to the size disparity of the brooks and browns. I'm pretty sure the large browns are chasing them around stressing them out. I've seen it before. Brooks I planted this spring are only 1 1/2 to 2 lbs. while some of the browns approach 5 lbs now even though they maxed out at 2 lbs. when planted in the fall.

Maybe I should stick with browns. My growth rate is astounding for them even compared to my suppliers.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.