I would avoid turbos, they die too easily. I use astrea snails. Instead of hermit crabs, I use sally lightfoot crabs. If you use hermits, the usual rule is one for every two gallons, and be sure to provide new shells for when they grow.For snails, one per gallon is the usual rule. Opinions vary, and this is only my opinion, but it works for me. I also have a sand sifting starfish. I just bought it, so I don't know how long it will last, but it looks great, when it isn't buried.