I just looked up the matrix product description on seachem's website, and they claim:
"...These macropores are ideally sized for the support of nitrifying and denitrifying bacteria. This allows Matrix™, unlike other forms of biomedia, to remove nitrate along with ammonia and nitrite, simultaneously and in the same filter. "http://www.seachem.com/Products/prod...es/Matrix.html
What an interesting claim; I just don't see how this is possible...
Time to e-mail Seachem support