Grr, I just lost what I typed to you. So here's the short of it:
Personally, Bio pellets are way too new for me to be designing a sump around their use. I haven't seen enough evidence yet - it seems to be hit or miss so far.
I would suggest instead of a refugium that you consider using that chamber to solely contain chaeto. Chaeto thrives on high flow. Be sure to keep things like live rock, other macroalgae, critters, etc out of the chaeto chamber so the chaeto ball can continuously tumble without hindrance. Also be sure to keep it well trimmed for the same reason. Good light, good tumbling, good flow = great nutrient reduction. Proven, reliable, and cheap! In fact, you can make a few bucks selling chaeto balls when you trim.
