ppht:
You may need to increase other means of nitrogen export to adequately reduce nitrate.
These articles may help you do that:
Nitrate in the Reef Aquarium
http://www.advancedaquarist.com/issu...t2003/chem.htm
Phosphate and the Reef Aquarium
http://reefkeeping.com/issues/2006-09/rhf/index.php