I agree with both previous posts. Pwc
's are the way to go! Even if your refugium works perfectly at removing your Nitrates, the depletion of all the other elements is hard-impossible to track, costly, exacting, and tedious. I speak from experience. I went from weekly changes on a 135, for years, to 2 changes in a year on a 180 w/ 30 g sock/ skimmer sump and 30 g refuge , with supplementation. Though trates weren't a problem, the lack of proper supplementation was, although I tried. Since then, I have done weekly changes with a good reef salt and things are back to normal. Honestly too, it's just much easier to do the changes, than constantly be battling levels!
A refuge should simply be supplemental filtration, more of a food factory w/filter benefits, than a necessary part of the filter. Still a great thing to have!