I just purchased a SWC Mini s Cone skimmer for my 90 gallon. I have the skimmer running in about 9.5" or water. I cannot seem to get the skimmer to produce any skim. I have had the skimmer in the tank for about a month and believe it should be broken in. It seems as though the pump is not strong enough for the skimmer. I need to close the valve on the outlet almost completly to get the skimmer to produce any skim at all. When I first turn on the skimmer if the valve is open all of the way bubbles rise up the cone like I feel they should then after about 5 minutes of running the level just drops and never returns. PLease help me figure out what is going on with my new skimmer.