White spots on hepatus

I'm new to this forum and would like to say hi to everyone here!
Now to my problem. About 5 days ago I've noticed white spots on my hepatus (blue tang). The first thing that came to my mind is that the fish has cryptocarion (white spot disease). But there's one thing that's puzzling to me: the white spots appear in the evening hours. What I mean is: in the morning and during the day the fish is clean, but closer to evening (about 8PM) the white spots would to appear... What can it be if it's not the cryptocarion? Did anyone have a similar conditions? I would really appreciate any suggestions!

Thank you for you reply! I will try to make some pics. But... It definitely doesn't look like a change in fish's coloration. At first glance it looks like ich but then.. Why would it disappear during the night and reappear in the evening..?

I really appreciate you input!

Amphiprion said:

.. or you could be catching certain parasites between cycles.

Click to expand...

And I think that this is the case. Just in case I've started adding No-Ich to my tank.