If you have any coralline in the tank, even on a snail shell it will spread. Just keep the water clean and provide some light and it will spread pretty quick.
I just set up my 180g about 2 months ago and had some coralline covered snails and one rock with it and its now growing on other rocks as well as the glass,
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.