Is there such a thing, within reason? I currently have a HOB filter running at 300gph on the back of my 36g bowfront. I realized my lid has a cutout space for an additional filter, and I'd like to add a second HOB, or a small internal canister with a few kinds of media in it. The second HOB would probably be rated at ~200gph or so, and would be used to quickstart a quarantine tank when I get around to setting a 20 or 29 up for that purpose. Any downside to this? The fish in this tank are fine with a strong water flow.