You can start wtih 2/gallon or about 20 nass snails (make suere they are vibex). You may want more variety though.
Cerith Snails-Cerithium spp. (Cortez) - Good algae and detritus eaters that forage rock, glass, and sand. Some can pick themselves up and some cant.
Cerith Snails (White)- Good algae and detritus eaters that seem to stay in the sand more than the cortez, but can be found on the rock and glass. Once again, some can pick themselves up and others cant. These are good sand bed snails.
Astrea Snails -Astraea tecta: Most common of all saltwater tank snails. They are excellent algae eaters and will forage all over the rock, sand, and glass. These guys fall very easily, can not right themselves, and then die.
From BlueZoo Aquatics:
"Adding grazing snails to your aquarium for algae control is heartily recommended as long as you don’t add too many, too fast (often resulting in starvation), you acclimate them properly, and you keep your water parameters stable.
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Acclimation
Drip method (Invertebrates: Snails, Crabs)
These animals will ship in much less water and are therefore easily acclimated in their original bag.
cut open (or off) the top of the bag to allow water from your drip line to be added and then secure them so they don’t tip over when more water is added
Often there is newspaper or paper towel to keep them moist. Create a drip volume that adds maybe one drop or less per second (see above). This should create about an inch of water over a period of one hour. For these creatures slower truly is better.
You do not have to discard any water like above. After one hour, simply add the animals to the sand bed by hand (do not put acclimation water into tank).
Snails & Crabs- may not open or move for days at a time- after this time if you suspect death pick them out of tank (if they smell bad, they're dead – don’t put them back)"
