FISH stopped eating but behaves normally

[Depth]

I have four fish in my 15 gal QT now, 2 damsels and two filefish. I am treating the QT with Hyposalinity for Ich. Salinity has been very low for 2 weeks now - SG=1.009. I know this stresses them out. However, everyone is behaving normally and eating voraciously - except the 4" red-tail filefish....
In the beginning it did eat some of the foods I offered. Then started eating nothing but live brine shrimp. Now, it hasn't eaten anything for a week. It has no other symptoms, Ich is not visible anymore. It is behaving normally, swimming very calmly etc., but does not eat!!

There is no aggression in tank, water parameters are excellent. Temp - 83 F (I have been raising it slowly to speed up the life cycle of Ich).

I know that I will most likely lose this fish - but I want to know the reason! The fish doesn't appear sick in any possible way - and everyone else is doing excellent! What can it be?

 

[Depth]

Also, one of the Damsels (who never contracted Ich!) has white stringy poo-poo for a few days now - but again, no other symptoms whatsoever. It eats great and behaves normally. Could the stress of the low salinity alone produce the white string?

 

[marrone]

By dropping the SG to 1.009 you're not stressing them out, specially if you do it over time. The fish will be a lot more stressed out from being keep in a 15gal container or having the ich then having the SG at 1.009

As for the file fish, they aren't the best of eaters to begin with and can be very shy. You're placing it in a small container with other fish and that could be the cause of why it's not eating.

Also since this is a QT you don't want to feed a lot as you're going to pollute the tank.