Feed live zooplankton and they'll eat live food if you have it in your system. I try to simulate natural food sources whenever possible, but I know people feed them reef-roids, but either way food should be micron size, not pellets. I feed 2-3 times/week in the evening.
You'll find everyone differs which is why when in doubt I do things as best I can in natures way.
For years Ive always fed my scolies and Acanthophyllia shrimp. Not PE Mysis but raw shrimp from the store that I prepare every few weeks for my fish. I chop it up REALLY well and whenever they are ready, every 3-4 days they will eat a nice size..
I mix it with reef roids and reef chili when available.