I'd run the air 24/7 if it's not costly but I'm not sure what your system looks like. My air moves solids to a center drain besides aerating the tank. I also use air to move my moving bed media.

I hear you on low water temps and tilapia. I picked a bad year to raise tilapia outside for the first time. I'm lucky to get water temps above the lower 70's and I don't want to crank up a heater in July!

I will tell you one thing: Tilapia are messy compared to the bluegill and yellow perch I've been raising in my RAS'. Lots of fecal casts!

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