YOu may want to use the 47g and still sell the tank as they should be in a min 100g tank but one can get away with a 90g tank, Nems put out alot of waist so you may want the 47g any way. did you get the 47g from a store or used? Just wondering because if it was used the problem could be with the tank its self and you may want to resilicone the tank and use it. I only say this because you say every thing is starting to bounce back quickly. So there maybe something leaching out of the silicone in the 47g, I would only suspect this if the tank was a used tank. I find that some fish are way more suseptible to water changes than others. Your polups should come back but may take a bit longer. they could be the problem did you give everi thing dips before putting them into the temp tank?
Bill