It's not by choice. I haven't had a chance to set up my ato. So, the water level is never the same. I like the skimmer to run in 8-9" of water. I think it only takes a couple of hours before the level is to low for it to really skim anything. The guy I got it from had a 32g brute can that was gravity fed into the sump with a auto shutoff value in the sump. I just need to make a platform to sit the can on top of and haven't had time to make something.