lol. good call woodstock
I agree with witfull, you need carbon in there. that filter is set up for it in the area where the water comes out next to the bioball chamber. You could replace the balls with live rock like wit said also. I see your in good hands here
I dont see where you could change it into a refugium so if you intend on keeping that filter id stick to just mechanical filtration. I myself have very little mechanical filtration and use a more natural method. Here's a pic for you.
Its a mud system i made. I grow carlarpa and am trying to grow mangroves in it also. i have a few pieces of live rock in there, some crabs and snails and a ton of other critters too. the mud is suspended to keep the gas pockets from forming letting the water filter up through the mud. I too had trouble with nitrates in the beginning but it seems to have gone down and al the levels have become normal over a corse of a few days and are holding well now. Just keep up on the water changes till you see the nitrates come down. and ditch the balls!