April 2011 fish magazine issue question.

[Gummy Walrus]

I lost my copy of a fish magazine, and forgot what company made it. It had an article on macroalgae forests, on page 76 there was a product review on s underground filter, (I want to know what that is...) and some where in there was a ad for a nitrate reduction filter (I also want to know what that is...)

Please,
If you know what those filters are called, that would help.

Thanks in advance,
Chad.