Yep....don't do filters like that. The only biofilter you need is live rock and live sand (even if you buy base rock and dry sand, it will eventually become live). You're better off investing in a good skimmer. Those canister filters are best left for freshwater. You can use them in saltwater, but it just adds more unnecessary work, imo, because you have to clean them out regularly otherwise they become nitrate factories. And if you change your mind later and decide to take them out, you'd have to do it slowly so as not to cause your tank to cycle.