i have about a 4month old jack dempsey in my 75 gal tank along with a pleco and a few misc fish. They are one happy family and it has been 4months with this tank and no problems. All of a sudden my jd went from jet black with one silver spot to almost bluish silver with a black spot. He is also just hanging around mid tank level and not very active for the last few days. He does eat like a champ and when he moves he is still fast and kind of aggressive , but something doesn't seem right. Normal water changes have been made and chem levels are all the same. Is this action normal or should i be worried? thanks, Dan