betta fish keep dying

Question
QUESTION: On Monday, my roommate and I purchased 2 female betta fish from Petco and were told by the "fish specialist" that they could live together in a fishbowl. They were fine for the first few hours but the next morning they were both dead.

We returned to Petco and were told by a different employee that the fish should not be together in such a small environment even though they were females. She tested the water and said it was fine. So, we chose one male delta tail betta who appeared to be very healthy which was new to the store that day...or at least that is what we were told.

We washed the bowl, rocks, and plant and treated the water and later put the fish in after having poured some of the treated water into the betta's container. We fed him a couple of pellets of betta food and he was very energetic, but this lasted only about 2 hours.

He was then floating at the top and had small movements and 45 minutes later he was on his side at the bottom, slowly dying. We called Petco and were told there's nothing you can do for him and just wait for him to die and get a new fish.

We purchased a fishbowl kit from Walmart and cleaned all pieces thoroughly. We put in the recommended amount of water and treated it for 25min.; then put some in the betta's container and let that sit for about 15min before placing him in the fishbowl.

Is there anything we can do to prevent this from happening again? Should we try a different store or are we doing something wrong?

Thanks,
Kathy and Jackie

ANSWER: Hello Kathy and Jackie:  I am sorry to read about your fish losses... What did you use to clean the bettas bowl and rocks, etc.???

---------- FOLLOW-UP ----------

QUESTION: We did not use any soap, just hot water.

Answer
Is it possible that something like a household toxin such as fly spray or something like that could have gotten in the tank???? The other option is that something may have happened during transportation...such as the temperature in the bag getting too high... Usually fish don't just die.... If the water is testing ok... then either the fish were sick or weak and couldn't handle the stress of transport, etc.... or something else is in the water that is killing them off.  The water test kits only test for a few chemicals and anything like pledge or bleach can kill fish really quickly and not show up on the tests.   let me know.... dave