Snails in SW
aquaria are nothing like FW
tanks. They are no where near as prolific and often do not bread at all. Many of the egg masses laid never get properly fertilized or are eaten by other scavengers. If your cocerned about the tank being overrun by snails, don't be. It will rarely, if ever happen
That said, snails will indeed be your best defence against aglaes as well as detritus. Here are a few good suggestions.
great for detritus and the sand bed.
especially good at film algaes..
cleans both the glass and the sand bed..
cleans up the uneaten food bits as well as detritus.
another excellent algae eater..
The amounts of each will vary on the types of algae problems or detritus as well as fish types you may keep. The general rule is 1 snail to every 1-1˝ gal
of tank water volume. In the beginning though I would start with about half that and build as needed based on the natural food sources available to them.