If I were you I would get another little tank going for growing snails. Pond snails and rams horn are your best bet. What I do is take a few snails and place them on the window ledge (not direct sunlight though or they will bake) and then put in some lettuce leaves every so often. They will have lots of babies in no time and you will always have some food for them.
Make sure the ones you buy don't have huge heads and hollow looking bodies as this is a sign that they are malnurished and will probably die soon.
Also ask the petsmart what they have been feeding them. If they say flake food then I would be wary of buying them. Puffers never eat flake food and will proabbly starve to death while looking for more food. Try to get ones that just arrived in the store.
