Hiya Scott
OK, Firstly, yes the Figure of 8's (Tetraodon biocellatus) will eat snails. They will struggle with the bigger ones (obviously) but are still efficient snail eaters.
They are brackish water puffers and ideally will need the salt levels constantly changing to represent the natural change in salt levels in the wild. They occur in the Asian countries in the wild, such as Thailand.
Eventually they will grow to about 3 inches tops. Although, various literature states different sizes, I always find about 7.5cm (3") to be the maximum. pH wise you need it between 7.2 and 7.9 - although this is not essential for this tetradon species.
When it comes to feeding you will need plenty of meaty foods such as bloodworm and krill. Also try to include harder-shelled meat like cockle, mussel and prawn - but be sure to remove any uneaten food quickly. Also, they will need snails at least once a week to keep their teeth worn down - but it sounds like you've got this covered!!
Anymore question - just ask!
