Is your goal additional biological filtration of ammonia and nitrite or are you also looking for anaerobic bacteria growth for nitrate control?
Both options presented work very well for for ammonia and nitrite performance. For nitrate removal they each need to be used in specific ways.
I'm a fan of matrix, but spoke at length with the Cermedia folks at macna about their product. Their booth was right next to JJs and they are Buffalo based (where I grew up). The product looks very very good and glad to hear Sirreals testimony. I was close to buying a block at MACNA, but didn't really want to bring it gone on the airplane. I may pull the trigger and toss one into my sump.
Sirreal, do you have it sitting on the bottom of the sump or raised up? They said it needs to be in a real low flow area for nitrate removal. I don't get how it can't collect detritus. You don't blast it off occasionally or have detritus build up in front of it?
...stupid auto correct