From my uneducated experience I have always let my nose tell me how long to tun aerators. I have 5 in my 2+ acre pond, Two in shallow water, 2 in mid-depth (8 - 12 feet) & one in the deepest part, (18+ feet.
Every year when I first start them I run my boat over each set of bubbles. If the air, on a calm air day, smells good I keep it running all summer 24/7. If the air smells bad I run it 15 or so minutes each day. I very gradually increase run times by just a few minutes a day until the air smells good. The first year or two it took several weeks before I ran the one in deep water full time.
