It is probably releasing zooxanthellae. Is it new, or have you moved it to a different light level or changed lights or bulbs recently? If so it's adjusting to the new light.
It has been in the tank 6 months. It is growing new branches and in water flow.I guess I will just keep an eye on it. It seems to be doing fine other then that. It does it right before the day lights go out.
Is it expelling the brownish goo from its mouth(s)? If so I would agree with DIBerlin about the zooxanthellae. If it is a brownish jelly like goo, I would be worried about a possible brown jelly infection to which Euphyllia are prone.
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