Best bet for a refugium is no sand just the seagrass I use and some rocks.. I have mysis, big pods, micro pods, and mini brittles in my 125 gallon sump/refugium.. If you add sand over time it will become a nutrient sink...
No, hold on to nutrients(nutrient sink),, the bad ones trust me I've been doing this for 13+ years without a tank crash, I'm good.. Look at my coral colors,,lol..
I'm selling all my refugium seagrass if you can make it out to SI.. 125 sump/refugium.. I could also show you some nice tricks to making a refugium do what it's suppossed to do