The new Classics are more powerful that the previous version with the OTP pump. This skimmer should sit in 7-8" of water and is intended to have the valve submerged. If your skimmer is overflowing it is likely to do with something in the water itself like bacterial products, dechlorinator, frag putty, red slime remover etc. It could also just be something within the rock or a bacteria outbreak common with cycling systems. Running a good amount of fresh activated charcoal will help as well as positioning the skimmer at 7-8" to obtain the greatest range of control from your skimmer. If the skimmer is overflowing uncontrollably you can continue to use it if you connect a hose to the drain line from the cup and allow the drainage to spill over or in a bag of GAC.