thedidavid, this same thing happened to me but cracked on opposite corners. I was lucky and was home when it happened. I was able to save all my livestock. I ended up buying another Red Sea Max so I could get everything put back together. I called Red Sea and they are also sending me a replacement tank. I, like you, have no idea why it happened. You can read my thread here,
http://archive.reefcentral.com/forum...25&pagenumber=