I had 30~ppm nitrates for a long time. I was recommended Nitra-Guard Bio Cubes from J&L, and within a week my nitrates were down to between 5-10ppm (which I like to keep it there.)
http://www.jlaquatics.com/phpstore/s..._ID=plb-ng0500
Works pretty well! Just put them in a bag and throw them in the back!