I run a 20 gallon refugium and algae scrubber on a 40g breeder with a number of acropora and other sps. I do a two 5g water changes a month and get really good growth on all my stony corals, but very little growth on many of my soft corals. I assume its because of the very low nutrient levels. My bio-load is pretty large with coral and fish. I tried running without the algae scrubber for the last two months and it worked, but some macro algae's started slowly growing in my tank so I'm running it again. I think element depletion is the biggest problem, but lots of crushed live rock in the refugium and occasional amino acid dose seems to keep the element supply in check for me.