So am I figuring this right. If I calculate the actual water volume of my display tank and then figure 10% of that for my refugium size? So if my actual water volume is 68 gallons in an 80 gal display tank I could go as low as a 6.8 gal refugium?
I think your calculation is correct, however, I have found so much benefit to having the refugium as big as possible, or as much as space permits, I think my refugium is somewhere in the region of 25%-35% volume. The pod population, the life in there, the added stability. I would try not skimp out on this area.