Motor....R u selling a unit? If so, I am interested in taking it off of ur hands.
I was kinda kidding..there is a rodi up on the For Sale forum currently.
If you want to knock the Nitrates down further you will want to do larger water changes..8-10g per week.
Make sure you get that muck/gunk/goo stuff out of your overflow. If it stays in there your trates won't come down. A turkey baster is handy for a task like this.