I added a Juvenile Melanarus on Friday morning. He was fine the entire day happily exploring his new home. Its now Monday and I have not seen him since. This is my 3rd Melanarus wrasse. My first Melanarus i had for about 2.5 years when one day he just showed up dead. Nobody else just him. I tried again about 6 months ago. Added the wrasse never saw him again after day 1. Could something in the sand be poisoning them? My average depth is about 4 inches. I really like these fish. I can't understand why suddenly I have a problem keeping them. Tank is 3 years old and parameters are all stable and well within normal limits. Any advice?