ok i got a hippo tang that i have had for around 7 to 8 months. about 3 days ago i noticed that its color was kinda fading. i guess the best way to describe it is that it sort of looks like it has marine velvet, which it has had once. but the thing is that when i turn on the lights in the mourning it will be fine. after a couple of hours it goes to the corner of the tank and constantly runs up and down the glass. once the lights go out for just a bit he calms down and color returns to normal.its eating fine all the other fish are fine. i feed it seaweed salad everyday. it also gets flake food or frozen mysis everyday and i feed live shrimp once a week. its a 135 gallon tank. theres the blue tang,yellow tang,2 percula clowns, greenbanded goby,lawnmower blenny,flame scallop,2 cleaner shrimp,alot of herimits, some snails and some corals in the tank. Nitrite=0, Ammonia=0, PH=8.2, Alk=2.2 the only thing that is not doing good is the nitrates, they are around 20-30 ppm, but they always have been. i use tap water and thats what they are straight from the tap. i know you guys are gonna say get ro water and stuff like that so let me save some time. im gonna continue to use tap water. no fish i have ever had has died from doing so. i have some freinds with tanks and they use tap water too and havnt had any troubles. and sorry if anyone takes that as rude. i just dont want to get into the R/O water vs tap water conflict. i really dont think the nitrates are the problem because they have always been there and this has never happened before. hope someone can help and thanks ahead of time.