The way I am setting my fuge up will enable it to have about 30 gallons. Bulkheads will be about 3" down from the top and the drain will be a piece of pvc
that is slotted with an elbow on the end of it to prevent overflows. You can see the refugium I am doing at www.lifereef.com
under custom work.
Will 28w still be enough?
Attached is a pic of the refugium type. Mine will be larger