mmm, this is a challenge isn't it? Well I am not master, but there would be two things I would try. First, I would try to just block that area of the light with some cardboard or my hand. That would eliminate the reflection but of course there would have to be sufficent light hitting the coral from the light to the sides or behind what you were blocking. Second, I would try a polarizing filter. they are designed to reduce reflections like that. I am not sure it would eliminate it though. Worth a try though.