Can you post a full tank shot with white lights?
I've had similar experiences with Niger Triggers in QT. If he's hiding near/behind something dark then that's definitely not good. I've seen that behavior with Nigers in the early stages of Velvet. But without a good visual of the tank and setup, I'm literally stabbing in the dark.
And ask yourself... What happened, what changed 3-5 days ago?
At this point, you've checked off two of the four key symptoms of Velvet, so heads-up!
- Reduced or complete loss of appetite.
- Heavy breathing, scratching, flashing, head twitching, erratic swimming behavior (unfortunately velvet shares all these same symptoms with ich & gill flukes.)
- Swimming into the flow of a water pump/wavemaker/powerhead (unique to velvet).
- Acting reclusive (velvet causes fish to be sensitive to light).