bettas dying

Question
hi david-
So i hava sixteen gallon tank which had 5 female bettas in.  They seemed to havebeen living together harmoniously with a nip here and there.  The first one died two days ago.  The second one died this morning and a third one is dying as  i write.  I have no idea what is going on.  They all seemed to be in top shape and swimming around fine and suddenly they are barely moving and periodically darting for the surface of the water to what seems to be like they are darting for air.  I checked all the levels of the water and everything seems to be within range.  The only thing i can think of was that i used this preventative medicine called aquari sol to prevent ich and parasites.  But i had used that last week and everything seemed to have been going fine.   I am totally at a loss to what to do and what i am doing wrong.  cant help but blame myself for the deaths that are happening.

Answer
hi fred.... I see this very situation a lot at work.  One day the female betta,a are good the next they all died.  They are more susceptible to bacterial infections and so when they start to get sick they need antibiotics.  I mainly use triple sulfate with them.  so that is what I would recommend that you do as well.  keep me posted...dave