They are more efficient and collect much less mulm and are somewhat self-cleaning, unlike canister filters or a bag in a sump or box. So, to DIY one is not an issue BUT the GAC should barely be moving other wise you just grid it up. If one wants to fluidize it more use SeaChem Labs Matrix but cost wise / lb or / l it s like the most expensive GAC there is. Matrix is very hard and is a spherical GAC, so less issues with impact breakage.