Brain coral help

How much flow do open brain corals like? The reason I ask is because I have a power head 750 pointing across the tank and down towards the sand. I had a small red and green brain that was in the place the power head points to and the tissue started to stay closed and it even began bleaching on top. I moved it to a low flow area and it has regained its color and the tissue expands. I moved a larger purple brain into the location the red brain was located thinking it was a larger brain and would like more flow to help it get more food. It was doing fine for about a month, now for the past two weeks it has closed tissue, begining to bleach, and is ejecting long brown stringy stuff that is very gooey in consistancy but thick enough not to disolve easily. Is that it taking a poo? So I moved the puple brain next to the red brain hoping for a come back. Here's a couple pics. And sorry for the long post with all the questions.

 

You want to keep LPS out of direct flow, they like low to medium flow areas. It may have been pooing.

 

Mine is in a low flow area. The tissue will expand and contract based on no good reason whatsoever. One day it'll be rounded like a dome it's so full, another it'll be spread horizontally, the next it'll be hardly inflated, and it'll basically be random between those.

 

Alright, I was thinking that was the case but I wanted to make sure from the smart people. Thanks again.