You said you were cutting back the flow to the skimmer with a ball valve? Why is that? Is it designed to be run with a pump the size of a Rio 2500? If so, its probably better to control the air flow going to it then the water flow. That can be accomplished with a piece of air tubing and a 29 cent air valve. Small adjustments to the air valve are all that is needed to tune the skimmer. I don't think a Rio 2500 is going to handle the back pressure from a ball valve very well.