I've had two long-term resident blood shrimp just disappear! They are large enough to easily see and there aren't any areas they could hide where I couldn't find them. I'm wondering (and worrying) if my large majestic angel or my large tangs could have had a snack if they were molting? I've had them over two years and no one has ever bothered them. Any thoughts? I have a 210 gallon tank.