I have 3 fish in a 70 l tank. 2 orandas which i have had since may and a black moor that i have had since june. they have been happy and healthy since i bought them but this past week one of the orandas has developed black/green scales and spots around the face and marks on the tail. i have tried fish disease treatment but it does not seam to have helped. any help or advice would be greatfully recieved.