Illness/Sickness: White spots on black axolotl!!

[ChelseaAxies]

He ate just fine a couple days ago, then today he didn’t eat and when I looked closer I noticed he suddenly has white spots all over him. This is his first time ever turning down food. I’m not experienced in what to do when they’re ill since i’ve never had an ill axolotl before. His sister is in the same tank and she is doing fine. Any advice helps, thanks.
I tried to take pictures of him but he moves away quickly when he sees light.