I'm no expert either, but here goes: Could be lighting, could be the water. I have the same corals (and others) and the same light fixture. My tank is shallow (12 inches deep), so keep that in mind. I run 100% blue and 60% white, and the corals are doing well. I have a monitpora that's grown huge in the time I've had it.
That said, I've read that the current orbit marine LED isn't the best on the market. I'll probably upgrade soon; don't know to which light, though.
If you ramp up lighting, go slow and not all at once.