ok my advice is that the nitrite spike was from what you said that you fed to much and it sat there. feed with the dropper as you said that works. do small (like 10-25%) water changes daily to make sure you're nitrites say down. what you did (if i understand correctly) is cloned your old tank. you took everything from there and added it to your new tank right? filter media and gravel and such? that's 2 methods of cloning in one, so you should be good.
IMO, the nitrite spike not only was from the extra food sitting, but the fact that maybe your bacteria colony wasn't strong enough to do the slightly extra bio load. after all it was strong enough to live off of the 25 gallon. it was put into a 55 gallon and needed to catch up. not fact, but just a theory or idea. i feel your tank will be fine, just keep a look out until you no longer get nitrites and do water changes when they get a reading on the test (if they do). as said, elephant noses are EXTREMELY sensitive, but i feel that you are doing good, just keep up what you are doing with the water changes when needed and use the dropper to feed it and everything will be good.
good luck with it and if possible please by all means post pictures.
i love these guys, but don't have a tank that i could put one in right at the moment.
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