Tang - Cloudy eye

This morning my hippo tang had 1 cloudy eye.  She is eating and acting normally.  She was fine yesterday.   From what i have read on Reef Central , this is non threatening and doesn't need to be treated?
Is that correct?   i have had her for 3 months.  Water quality is good and my parameters are normal. 
 no one is picking on her and she is her normal friendly self. 
Thoughts?
Thank you
Mary

 

i feed a small amt in morning with main meal in early evening...

Rods food supplemented with'
Zoe

on odd days mysis shrimp with Rods

and nori is pretty much available all day