Why do my GFO granules do this? Tumbling on the bottom and a big clump on top? I finally put a filter sponge on top of the media because the top of the cartridge clogs with fines and eventually I lose most of my water flow through the chambers. Do I need to try a different kind of granule? This is Phosban. I read somewhere about someone using pelleted GFO. Would that work better in a media reactor?