Hey Kristy and Mike! I didnt want to say anything before this but ill tell ya now.

Do you have any emerald crabs in your tank?

When I brought home Hanz annd Franz they both attacked my Diamond Goby early in the morning before my lights were on. I watched it with my own eyes. This happened after about 2 weeks of having them. They grabbed the Goby's tail while he was sleeping and they started to eat his fins. It totally caught my by suprize! When the Goby woke up he tried to swim away and he couldnt Hanz and a good grip on him and I had to intervene. Sad to say the Goby didnt make it :( but its okay. I keep Hanz and Franz well fed now! I did some research and I found that when emerald crabs get bigger they are known to have a taste for meaty foods.