Hi everyone, i noticed one of my guppies was off color the last week, tonight i looked at her again and she has changed to a dark black color, she was a clear color guppy. She is not well, i have had her over a month i think. All the other guppies in the tank are good. Tonight i did a full water change and washed the rocks, i could not avoid this because i dont have a rock vacuum and there was food in the rocks. The tank had been set up a few months. Have you any idea what would turn my guppy black? Should i do a water test now after i only change the water an hour ago? How can i save her?