I've been on 0 for a while now, maybe a little higher but never anything over 10... I do weekly water changes with good reef salt. I would suggest more frequent water changes? Also, I don't have personal experience with them but I hear canisters will need to be cleaned good weekly otherwise they're nitrate factories. Not sure tho
You have to be very diligent with cleaning canister filters. They accumulate a lot of junk.