I'm doing weekly water changes and have a sump that is supplemented by an Eheim cannister - yet, I still get nitrate levels of about 40 after a week. Can anyone tell me if they have used a sulfer (or regular) denitrator? I have seen some DIY videos, but i'm a technical moron so I would like to go with a stock product like Kerallin, Aquamaxx or Seapora. Any comments?