The bacteria will level off on it's own.
I'd have to think it would cost that much to heat one of the IBC tubes for Tilapia. I'd think most like the same cost as heating your aquariums.
The tubs are filled with 200gals of water. The water is constantly pumped into the growbeds is a big heatloss. I prob need 2 500W heaters per tub to keep the water temp at 80F. I don't feel like investing in heaters.
The temp in the garage is at night now 70F and during the day 74.