I recall back when bioballs and wet dry filters fell out of favor in the reef hobby because of nitrate build up concerns. Of course this was not too long after I got a brand new Amiralcle PL-2000 wet dry filter with integrated protein skimmer back in the 90’s (cutting edge back then).
Now we see issues of ULN where people are dosing stump remover to increase nitrate levels as to not starve their coral. I’m going to add some bioballs to the filter sock of my Tunze 9410 skimmer to serve two purposes, one being to quiet down the noise of the outflow of the skimmer into the sock and the other to see if I can help raise my nitrate levels in any meaningful way. I would rather not use Marinepure or Siporax based on Aluminum leaching concerns.