This is the problem, too much linear flow. Try to get random flow and do not point the PH directly at the coral as you can shear the polyps off the skeleton.
I have done this on Wee man's advice basically above the unit. I have quite a bit of random flow as I have 2 x m1100 blasting into the reef structure and another 2 x m1100 blowing across the top, with the return pipe right in the middle.
Any other ideas of creating more random flow ?