I don't keep any hermits in our refugium. I do keep a few snails in there, but it's literally only 2 - 4 in a 20 gallon refugium (cerith and nassarius). There's others, of course, that I didn't add... like those tiny round shell snails that find their way into a tank via LR purchases.
I do have a word of caution though... Turbo snails are not the best choice for a refugium. I was having problems seeing any growth of our macroalgae in the refugium, and started to see our macroalgae disappearing without the color fading out or anything. Then, I figured out what was happening -- I saw the turbo snails eating the macroalgae. At first, I thought they might just be cleaning microalgae off of it, but further observation showed that they were in fact eating it. It's no wonder I couldn't notice any growth of the macroalgae. After removing the turbo snails, macroalgae growth has been great.
