Three layers will work well and you have to have a restrictor in the male thread that is half an inch, then you will get your serious air. So its going to take a female fitting on the front of teh cover with pvc tapered down to 1/2" before the air injector. You do that and you'll get the sicce to perform well. If not your only going to get the 20-30scfh.
Here's the way to get 22-24lpm out of your sicce's. I would suggest purchasing it if your not diy savy but if you are it will take a few bux from your local hardware to make. HTH
http://www.protein-skimmer.com/shopp...itemdetail.asp