The pump in the A/G is a water pump and as far as I know it stays on as long as the A/G is plugged in. It may cycle with the lights but I'm usually asleep then so I wouldn't know. The one that feeds the air stone is an external aquarium air pump and the only thing I use it for is to oxygenate my nutrient solution. I cycle it off at two hour intervals to give me a chance to do a little maintenance and give it a rest. I mean how much do you expect for something I paid six bucks for at Wal-Mart? I guess we all have our quirks, but it works for me. Hank