fish changing color

[matrixinc]

I have a 110 gallon marine tank. Bought it used with fish in it. transported to my home and refilled it with man-made salt water. I have been testing it everyday for Ph, Nitrate, ammonia, Nitrate.
Ammonia and Nitrite are currently present in small quanities. I have addeed some LFS recommended stuff to help me control this problem. Last night ny yellow tang changed its color to almost pure white. It happened suddenly and this AM it is back to its normal radiant yellow. Can this be from the chemical problems?
Other fish I have in the tang include 4 damsels. I have a bak bac daul protain skimmer , and a magnum 350 running with charcoal and machanical filter.
thnanks

[MonoSebaelover]

Welcome to Aquaria Central! Actually Yellow Tangs fade in to white in the evening probably to blend in better with surroundings possibly and then retain their Yellow color in am. It sounds perfectly normal BUT watch for ich if there is ammonia and nitrite present. Tangs are very picky about these two compounds and they hate them when they are present.