Here's a thought... and I do this with ALL of my SA/CA cichlids..
Take him out of the 135, and put him in a different tank.. Put whatever fish you want in the 135 (size appropriate to the midas), and after a few days, add the midas. The other fish have had time to make their territory, and the midas is less likely to be territorial.
I have my 11" midas with a Jag, Red Terror, RTM, and 3 juvenile barred midas with bichirs. He has definitely calmed down a bunch with this method.