Okay, I retested PH. Before I put the fish in the tank yesterday, PH was 6.6. Tonight it was 7.6!!! How does PH change that fast in a tank? I did a 20% water change and that brought PH down to 7.2 - which will probably kill off the remaining tetra, i know, but I just don't understand how PH can change that much with water in the tank. All I have is one measly plastic plant, gravel and a dora house for decoration from a fish store.
Anyone ever have this before and what did you do about it?
Thanks