I’m sorry you lost your beloved fish, it’s never easy.
If you do decide to try it again, would it be possible to put Toni in the 55g for a day and let the newer fish take claim of the 125g and then add Toni?
Ime the only way to add cichlids to an established tank is lots in one go, adding one or two will normally result in deaths, adding six and then reducing to the desired level after a few months has been successful for me.