Scrubbies are good, and I also find that filter floss (also called polyfill) is an excellent media not only for housing a high concentration of BB but it is also an effective clarifier, trapping a great deal of minute unwanted particulate from the water coloumn. It can be purchased at any fabric discount store where it'e usually called polyester quilt batting. For $5. or less you'll get around a one square yard roll - that much lasts me a couple of months at least, replacing it often in my 2 AC 110's on my 75 gal. Just cut it to whatever size needed to fit your filter(s), and double,triple, or even quadruple layer it. I remove the bottom layer or two weekly, (the dirtiest - & it does get very dirty quickly) replacing it on top with new pieces, thus preserving most of the BB that are in the other layers. Works very effectively in HOB filters, but a caution - it may tend to clog up some canisters. An good inexpensive media.