this is the design i just built, it's only a 10gal but you get the idea.
I would move the baffles that are on the left of the skimmer to the other side of the refugium, that way you aren't sending bubbles back to your main tank.
I would also get rid of the liverock area and move everything over to make a bigger refugium area and put the liverock in there. that way you get more sand room and macro/micro algae room also.
Hope this helps