I have had my blue hippo tang for about 2 weeks in the past 2 days his been gettin lighter in color on the bottom of his body does anyone know why this is happening or how it can be treated?
How big is he fish? Medium to large hippos like more swimming space then 4 feet...assuming the animal is in your 55.
He could just be settling in and still a little stressed. Try adding some vitamins to his food.
Does sound like stress to me. Also, check your tank for satry voltage due to faulty equipment as tangs are very sensitive to this.