Hi, we had recently bought a small blue tang. We already have a bigger blue tang in our main aquarium. Today, we added the small blue tang into our main aquarium and they seem to be pretty friendly with eachother. The bigger blue tang does not seem to bite the smaller one or show any agression towards eachother. But, there seems to be a problem. We have noticed that sometimes when our bigger blue tang goes to swim with the smaller one, he seems to turn a grey-ish white mostly along the black parts of his body. Then after a while, the grey-ish white coloration seems to fade away. We wanted to know what some possible reasons are for this occurance. Thanks!