Sounds like a 12 hour on/off cycle would be enough to maintain decent DO levels in deeper water if anoxic chemicals and low DO levels don't start showing up for 3 - 5 days.
I am experimenting with 4 hour cycles with a timer as follows: on 4 a.m. - 8 a.m.....off 8 a.m. - 12 noon...on 12 noon - 4 p.m...off 4 p.m. - 12 Midnight...then repeat. This gives me 12 hours of aeration broken up into 4 hour blocks over a 24 hour period. If I can find a temp probe I will be measuring water temps per Bill C's recommendation to see what variance I get at 22' (depth of difussers) vs. surface. I understand that's not as accurate as a DO reading, but it should give me some indication of aerobic activity at difusser depth.
