I bought a 5 gal pail of charcoal on EBay for 30 bucks. The guy had two tons for sale. Activated charcoal of almost any stripe will work, if unused. There are two parameters to consider, mesh size and moisture content. For example, mesh sizes run 8 X 12 or 4 X 10, etc. These correspond to something called "standard mesh sizes" which carry a single index number like "12". I think Bauer sells 8 X 12 or something close to it. You are looking for granular charcoal with a particle size of anywhere from 1/4 inch to 1/8 inch. The smaller size is better. I believe moisture for commercial AC runs 4%. Anyway, the charcoal which I bought had been sitting in a shed exposed to air. So, when I need a couple quarts of the stuff I heat it in an oven at about 300F, not too long as heat could change the character of the adsorbent.