Is it a possibility there is harmful bacteria in the water?

Question
Thank you for being so prompt on answering my first question!!!!!!  

 Is there a possibility that there are harmful bacteria in the water? The reason I am asking is the fish that died would be fine one minute, then the next they would look disoriented. they began hitting the side of the tank, swimming like they were drunk, and then they would just die. On some of them there bellies would turn white, some would not. one fish just became motionless, but then it would be fine. It would repeat the routine several times... then it just up and died. I don't know if bacteria is or was the cause so I thought I'd ask. Thanks again!!!!!

Answer
D.C.

Sorry to hear you are having problems. Unfortunately, i need some more information. First off, what kind of fish do you have. How big is your tank? What are your water readings? What are you feeding them? Is it a cold water tank, or tropical? As soon as you get me the info, the sooner I can help you figure out what's going on.