I have my diffuser set 24" off the bottom and run it from 11PM until 7AM. I do turn it on 24/7 during the summer when a strong cold front comes through and I'll keep it running until it warms up again and the weather stabilizes. I've seen summer cold fronts disrupt the algea bloom and cause a DO sag, when the water goes from greenish to brown it's time to run the diffuser full-time. Night time aeration is a good idea when it's hot but watch out for cold, rainy, overcast weather and adjust for it. I am currently running 24/7, we had two weeks of hot weather followed by a really strong cold front, I am still waiting for temps to warm up before going back to just running it at night.