Fish are dying after water change?? PLEASE HELP!

I've gone back and re read the posts. Thank you SubRosa for the suggestion. My tank will now get a 50% water change every week.
What some of you don't quite understand is that I've always done 100% water changes (leaving a bit at the bottom) and there were no issues up until now. The fish were only in the bowl for about 15-20 minutes...could there have been too much ammonia in the water? Or not enough oxygen?

It is possible that something changed in your tap water. Mine doesn't stay consistent here, and at times, municipalities do maintennace on the systems and generally shock them with different additives. My tap ammonia is currently running at 1 ppm.
 
I do agree with SubRosa (post 10) that this could very well be the reason, but how would that explain why they started dying in the bowl?

The shock from your tank water at low pH and then in tap pH affecting the ammonium....
 
My family has had tanks as long as I can remember, and I finally got my first one as an adult. I went by what I had observed growing up as standards on how to keep and maintain my tank. Eventually it lead to problems and I found this community when I was looking for help. At first, these people sounded crazy (no offense!) with all their equipment and maintence. It sounded so over whelming! But, rest assured most everyone here knows what they are talking about!! After some research on my part, and finally testing the water periodically, it all made sense.

All that said, listen carefully, and take it one step at a time! I hope all works out and your remaining fish are ok! :)

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I do agree with SubRosa (post 10) that this could very well be the reason, but how would that explain why they started dying in the bowl?
It's simple really. Because the pH was very low, ammonia excreted by the fish accumulated in the water and the fish as ammonium which is almost non-toxic compared to ammonia. If the fish was exposed to a concentration of several ppm for an extended period, as is quite likely, a lot of ammonium built up in the fish. When you did the massive change the pH shot back up instantly to a level at which the ammonium converted back to toxic ammonia before it could be metabolized, poisoning the fish. Again this is all conjecture based on prior experience.
 
Thank you all for all this information! It's really great to find some nice folks who can help me out. My remaining fish are doing very well. I won't ever be keeping so many in one tank (though all of them were won at the carnival..LOL) and it looks as though I have some research and shopping to do! I am going to get a water testing kit so that I can test the levels of everything.
 
Yes stephybaby88, it is quite over whelming, and that's exactly how I feel! I thought I was doing a good job caring for my fish, but obviously I don't really know as much as you all here! It's very strange to hear all this about machines and levels and such...but I do want the best for my fish and I'm going to strive to do that. I'll keep you all updated! I will probably have more questions about the proper water levels...off to do some research! Wish me luck!
 
The Important thing is that you are taking the info, processing it, and seeking to improve the care you provide. :) My family kept tanks when I was young (basic fare, guppies, some swordtails, etc.) and it was basically 1) Change water with siphon 2) Change filter pad 3) check pH. I came back to the hobby as an adult and had to learn about this mystery "cycle" everyone talked about, different fish aggression levels, bioload, habitat zones, all kinds of good things. You're in the right place, and you're asking questions. That's the first, hardest step. After that, it's just following guides and advice. :)
 
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