I have a solids filtration system in the form of one 55 gallon drum as a radial flow filter flowing into a 55 gallon drum swirl filter and then into the sump tanks. I do not have bio balls. My thought was to reuse the expanded shale I already have as a biofilter in the bottoms of the new raft tables. Would I be better to use a couple of drums filled with the shale and and run air into the bottoms as a bio medium?