Well, my refugium is in my main tank, so to speak. I grow Calurpa, and harvest it about every three weeks. And yes, I even have hair algae in there. It is FULL of life that multiplies and feeds the tank. I never add anything to feed the corals and they are growing and even my Gorgonium is growing new branches.
I was experimenting with this tank, and so far it has been my most successful reef. I let the tank take care of itself. No filters, not even a skimmer.
IMHO, most aquarists today strive for the near impossible, and quite unnatural. A pristine tank with no algae. Then they dump quarts of food and additives into the tank. My tank today is feeding itself. All I have to do is export the excess algae to keep it in check. I am a huge believer in refugiums, wheather in the tank or not.
Sorry, I digress.
As far as Southdown Sand is concerned, I have no personal experience. But there are many reefers using this stuff out there, albeit the jury is out, as the longevity has yet to be really tested.
HTH
Hermit