I've never used an ATO. So just a quick question. I do not have a sump, this is an all in one tank. So when I do water changes the water drops in the back chamber. So of course the ATO starts pumping water. I've been turning off the ATO to do the water change then turning it back on when I'm done. Even though the water is at the right level the ATO freaks out and starts pumping water, and not a small bit of water, almost a liter. Since by now I have figured it's going to do this I just let it fill up my bucket until it quits. The unit works perfectly otherwise. Does any one have a work around? Am I missing the obvious? Much thanks.