The powerhead is rated at 530 gph at Hmax 1.8m and is sold in combination with an unbranded protien skimmer. Not sure what kind of flow you would actually be getting out of your return, but probably less than 300gph. I agree adding cans until you can rework your plumbing and run a higher output pump would be the quickest route to solving the ammonia and nitrite issue. You already have lots of ceramic media you can add to the canisters from your sump.