Also what is your calcium and alkalinity levels. Rule of thumb for any supplement, if you dose it, test for it.
Open brains usually don't do well if they are sitting on rock. They need to be sitting on sand at the bottom. Are we talking about a Trachyphyllia, Wellsophyllia, or another of the "open brains?" Maze brains can be a challenge depending on what species they are. Platogyra have a fairly low surival rate in a reef tank. There are other members of the Favia family that are commonly called "Maze brains" that do much better.
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano