MABJ is giving you fantastic advice and I suggest you listen to every word of it. Try to see if you can try to find a better home for the fish in both of those three gallon tanks. Even if you think the neons in your 3 gallon are thriving, they would really be very happy in atleast a 10 gallon. So I would do research about cycling, read around the forums and upgrade your tank to try to get a fresh start.
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