I have my seaclone in a ten gal sump (10gal glass aquarium). Originally it was sitting in about 8" of water and I noticed it was not skimming at all. I then raised it up about 4" by sitting it on a shelf I made and now it works fine. No real modifications to the skimmer other than taking the HOB stuff off and connecting the PH directly to the skimmer. What I was told by several people on this board was that the PH can't siphon enough airflow if it is more than 4" under the water surface. Kind of makes sense since when used in the HOB mode the PH is just under the surface of the water.