Foxface loks very bad after feeding!
 

I purchased a juvenile Foxface from lfs. Put it through TTM. Now in 20 gallon QT. After every or every other feeding this fish will turn from yellow to almost all black, stick its spines straight up, hide behide heater and look as though its going to die then 5 minutes later its normal and swimming around as if nothing has happened. This fish begs for food like it has never eaten before and when food hits the water it will devour it in seconds. I have tried Flake, Marine A and Spirulina Brine Shirmp by Hikari all of which it loves. Please help!

Ammonia: 0.0
1.024sg
78 degrees
Hang on filter and power head, bare bottom with 2 pvc elbows
Ligts: none
Medication: none except Prime and Stability

What you are observing is a normal stress reaction. Foxfaces can be pretty skittish, and this skittishness is magnified in a QT. As long as it is eating and otherwise behaving normally, I would not be concerned.

What he said

Before and After Pics
 

The look before and after. He has been in this bad state longer after eating.

My yellow tang also seems skittish and breathes rapidly at times in the quarantine.