I moved my swordtail into my 60 gallon goldfish tank because I thought I was selling my 20 gallon and I didn’t want to re-home him. I found a temp that would suit them all and introduced one fantail goldfish. They seemed to get along great! I recently introduced two more fantails and now the swordtail hides all the time. I didn’t end up selling my 20 gallon after all and have harlequin rasboras in there I am currently treating for fin rot. Once the treatment on the rasboras is complete should I move my swordtail back into the 20 gallon to be more comfortable?