There is no other filter box? Matala filter pads work great. I am helping someone with a skimmer set up real similar to yours. They have a bunch of the green matala pads in the skimmer box surrounding the pump. http://pond-supplies.thepondguy.com/garden/Matala-Filter-Pads I don't do filters or submersible pumps in skimmer boxes. There are others on here that do. Let them chime in also before you buy stuff. All of my ponds have been filtered with bogs and plants.