Yikes...what's happening to my tank?

[Carrera75]

I highly doubt that tap water killed his fish...I have been using tap water for 9 months and my tank is thriving! When I do a water change, I mix the water and do the water change right away.....I know a lot of people mix the water for a day or even for a few days but I have never done that. So far my tank is looking pretty good. I think there are a lot of thing that happen and are very hard to explain why they happened. Most of the time we guess but we don't really know the real reason why something happened.