I moved my fish to a new town and new water source. One of them was at least 2 years old and the other is a lot younger.
I emptied the water out in my move, but left the gravel with a little of the old water in there. I had a biological filter, etc and replaced none of the media after the move. It's a 10 gallon tank, divided, heated, filtered and one fish on each side.
I noticed one day after the move the older fish's gills were labored. The younger fish looked unaffected. I did an ammonia test - 3.0!!!!! I have done full water changes before and never had this problem. I bought some Kardon Ammonia Reducer yesterday and treated the tank. When I woke up, the older fish was dead.
Does water changes like this cause ammonia spikes? What can I do to bring it down?