Destruction of Zoa colony

So I finally got some zoas to take off and seemingly successful in my tank. I had a small colony of about 12 polyps, and it seemed as though they were ready to start multiplying. Last night, I had some polyps floating around, and noticed that the entire colony had essentially been destroyed. Talk about upsetting. What in the tank would just destroy an entire colony out of the blue like this? Nothing new has been added, and they have been in the tank for about 2 months. In the tank I have a hippo tang, yellow tang, mandarin goby, 5 blue-green chromis, 2 maroon clowns, and numerous snails and hermits. The night of the destruction, I did notice one of my crabs eating an apparently dead snail, not sure if there's any relevance.