So I've had a yellow tang for about a week along with a tomato clown, blue puffer, and a brittle star. She has been doing fine, no fighting or anything, but the other morning with I woke up she was really white on her sides. I asked a guy at the pet store and he said that's normal, they lighten at night. However, I have noticed she has stayed between the live rock all day today. I do not have a quarantine tank, I only have a 35 gal, so I put her in a small breeding net along the side of the tank thinking maybe she was just stressed. After I turned the light off for them to go to sleep, I looked about 1hr later, and she now has a black spot on both her sides! ??? I have no idea what it could be! I hope she makes it through the night :'( If anyone knows what this could be, please reply! I've looked up diseases and stress online, and I've just came upon black itch, yet she only has a big black spot on her sides! HELP!