Oh, dear. Do me a favor please. Go here and see if you can find which one it is:
http://pufferlist.com/ This is really important.
EDIT: I suspect what you have are these:
http://pufferlist.com/puffer/freshpuff.php?puffid=4 The common name is South American Puffer, or SAP for short. Like all other puffers, they should not be in a community tank but should be in a species only tank. Even the very smallest puffers can shred the fins of a much larger fish in less time than you might believe. And while they can sometimes get along with others while very young, as they age, they become MUCH more aggressive and can shred a tank mate they've grown up with and known for a long time. Most can't even be kept with their own type for long.
However, the one main difference between SAPs and other puffers is that they chronically suffer from overgrown teeth which can cause them to starve to death if not abated. They need to be fed a daily diet of hard shelled items such as snails (any kind except
MTS, Malaysian trumpet snails - the shells are too hard and will break their teeth), clams, mussels, etc. Other foods can be found here:
http://www.thepufferforum.com/articles/puffer/food.html
I highly recommend returning them to the store. Even when fed the appropriate foods, you will more than likely have to do dental work on them every few months. This is precisely why they are only recommended for experienced puffer keepers. Dental work consists of putting them to sleep and filing their teeth down. Great care must be taken in putting them to sleep, as one drop too much of the clove oil that is used can instead kill them. And because they are so small, there's a very real danger of crushing them while doing dentistry.
Additionally, puffers should NEVER be out of the water. NEVER use a net to remove them. If you do return them, which I highly recommend, please use a cup or some other similar container. They can and do regularly puff when exposed to the air. If they puff in the air, they can and usually do die.
Please let me know if you have any questions or concerns. Puffers are a very big passion for me and I've done quite a lot of study on them because of that.
