I;m not sure of all of your critters but at night, when the poyps are "closed" try looking in at the base of them for a few critters.
1: look for a snail It has a round flatter shell with a cherboard pattern on it. The name is sundail or "Heliacus" if you want more specific. It is a common hitch-hiker in button polyps and yellow polyps. It is predatory. When the snail pulls into its shell it will cover its "foot" with a conicle trap door.... the whole thing will be smaller than a button.
2: look for any crabs you didn't buy.... pointy claws.
3: small star-fish. Some of these dime size critters seem to completely ignore corals. Others SEEM to feast on them. IMO if they are amongst the corals.... they go away. If they are on glass, sand, rock I leave them alone.
Also I have heard on some occasions tha bumble bee snails will eat yellow/button polyps.
Good luck.