by any chance you are using Instant Ocean salt?
if so, is it a new box you recently opened?
How long have you had it? It can take as long as a month to show symptoms of sickness. Also, don't worry too much about what it looks like at night, especially in the dark. If it stays like that for an extended period time during the day, then I would be concerned. Finally, have you checked for cuts marks or scars? In the photos above, look in the 12 o'clock position on the nem for any odd marks.