Need Opinions

I am running a Trigger Systems Ruby 30 sump on my 75 gallon tank. From stage 2(refugium) to stage 3(return pump) there are two trays that the water goes through. The top tray has a foam block and the lower tray is currently empty. I was thinking of putting some Seachem Matrix on the lower tray to help with nitrate removal. Just wondering what the opinions are of this product? I am also having an issue with micro-bubbles and was hoping as a side effect that going through this media would help to eliminate these. Just to fill you in on the rest of the sump. Stage 1 has filter socks and protein skimmer. I also have a reactor running ac and gfo going from stage 1 to 3.

 

Anyone??