i'm not using any air stones. i felt like the misters added enough air to the water. maybe i'm wrong with my assumption? i have 10 ez clone misters backed by a 500 gph pump. it's not variable. i'm not sure what that means exactly but i'm pretty sure the pumps nothing special. i got it at my hydro store if that helps. i'm going to pick up a tank heater tonight. anything special i should look for?