I lost my bimac that I've had since November a couple days ago for no known reason. He was acting fine and attacking his feeding stick like normal, then I released a crab into his tank and he went after it. He grabbed the crab and started moving to his den when all of a sudden he stopped, dropped the crab which was still alive and started convulsing and wrapping his tentacles around himself. Then he went to the glass and looked like he would be ok, but when I went to check on him minutes later he was dead. The crab came from a reef tank, so I don't think copper would be the problem, has anyone else experienced this before or have any ideas of what could have caused his sudden demise?