I have only about 3 inches in my refugium and i'm happy with it. I do however have a 6 inch sand bed in the main tank though. Not sure if you want to go with a dsb
in there as the smaller square area will not provvide much benefit from what I've read.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.