On Saturday my purple monti that I had been searching for for ages and have had for about 4 weeks was looking good and I was very proud of it. On Sunday at about lunchtime when the lights were fully on I was showing it to @butcherman & @Hails when I noticed the huge Munch marks on both sides of the coral. We pulled the coral out and there was a small starfish on the coral plug. We assumed that this is what was grinding away at the monti. There are a few flat worms in the tank but i don't think flatworms will grind away at the coral skeleton. Here is a pic of the coral showing the damage to both sides, that I took a little later in the afternoon.