The only predator that you have to be concerned about for plating Montipora sp. are Montipora eating Nudibranchs. They are very very small, and typically white. You may see what appears to be microscopic grains of white rice piled up in a spot, and these are probably nudibranchs if they don't blow off like grains of sand. The nudibranchs lay their eggs on the underside of the coral, and as soon as they hatch they'll feed on the live tissue of the colony. I had an outbreak in my propagation tank that grew out of control in no time. Once I recognized what they were, I could siphon out 200 a day and still not keep up. If you see two nudibranchs together, odds are they're laying eggs. Further information here. NOT reef-safe!