Well, i now know why.
I was sitting down by the tank adjusting a calcium reactor drip rate, when i stood up the fish got spooked and darted away. On its way it broke a large colony of SPS coral that was almost half inch in diameter and didn't even get a scratch ! (well may be a quarter of an inch but still amazing)
Here is that fish for sale if anyone wants a true HIPPO LOL !
http://www.canreef.com/vbulletin/showthread.php?t=98664