Open brains are very suseptical to damage of the soft fleshy part over the septars. if the brain has been damaged you could have a bacterial infection, if coral is not damaged you could have cynobacteria, or expelled zooxanthellae. could be something from else where in the tank if on the out side. could not tell by pict posted. not clear enough. can you tell if the soft tissue is damaged?. hope something here helps. The bright red specimens generally are from very turbid water, or they were shaded by an overhang or adjacent coral. they fare best at the bottom of a brightly illuminated tank. the red colour is indicative of green light usage. the use of a green flourescent bulb will enhance the colour and health of the specimen, through green light makes other specimens appear less colourful. Trachyphylia geoffroyi is hardy . iodine (as potassium iodide) is expecially critical for the health of trachypyllia. symptoms of iodine deficiency are sudden bleaching accompanied by poor tissue expansion, and inability to adapt to a light field. should be fed small pieces of fresh shrimp at night when tentacles are extended. weekly feedings will help. good luck. hope the brown is not a narcosis/brown jelly or other infection. wish i could help more but pic not good enough for me to see what i need to see so the above is just fruit for thought. hope something helps.