I have to agree with shrks1fan, i am not surprised they are dying either especially seeing as though you got one from Petsmart.
Where I live in Wakefield all our petsmart stores were taken over by pets at home and I have had loads of coldwater fish from this company and in one instance I brought a lionhead home and within a week I had lost the lionhead and about 5 other fish which I had already for 2-3 weeks prior to introducing the lionhead. Because Pets At Home offer a replacement service on animals bought there i was going to replace my lionhead with another one, when I went to look at them to choose which one I wanted they had all been taken off sale and were being treated. They were all acting the same way all my other fish had done before they died. I have to say though they did replace ALL the fish which had died as they admitted that it was likely to have been the lionhead which caused all the deaths in the first place.
I no longer buy fish from superstores like this if I can help it, i have 2 great lfs's near me, one called Interfish and one called Pisces. I have never had any problems with either of these suppliers and as far as I know they get their fish from different suppliers to places such as petsmart and walmart. (I know pisces definately gets his fish from a reputable supplier and his supplier quaranteens the fish for a week before the guy can go and collect them.)
I have bettas and have got them all from these 2 stores with not one casualty.
I suggest you find a new fish supplier and sooner rather than later.
Before getting any fish from any store it is best to look at the condition of the fish and see if they are acting strange at all in the tank and when you do get them don't forget to introduce them slowly to your water by floating the bag and introducing your water and some stress coat and then release the new fish about 30 mins or more after getting it home and aclimatised.
Kaz
P.S sorry for the long post.