hmm...how "well" did you clean it the first time you did the water change? How big is your tank? You did a gravel vaccum right? How much of the water did you change out? And how long did the tank go with no water change?
My guess is that you went quite a while with no water change. Then, did a really good, a too good, water change, and got rid of all the nice bacteria in the water. This might have caused the ammonia in your tank to spike as well..
Also, the fish going from a tank full of nitrate, nitrites, etc. then going to a tank with none, might have shocked it. Do you have a test kit now? Test the water, and let us know the parameters (nitrate, nitrite, ammonia, ph
, etc.) and we should be able to help you.
Sorry about your loss, by the way. Good luck!
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