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Aaron I also had bioballs in my wet/dry and over time removed them and put in rubble instead. I also use the pura filters you described in my drip tray. Here is a link to the cheapest place I have found the polyfilters. http://store.fishsupply.com/s1ppb-04080.html
I found the poly filters at an LFS over the weekend and did not but any. For the cost I can get the Pura filter for less and have been happy with them. I also noticed they said nothing about removing nitrates.