Fish disease/symptom not fitting any Profile?

[Veosk]

I've lost a blue throat, yellow tang, and powder brown tang one at a time within the past 3-4 weeks. Each fish so no signs of illness. It starts with hiding. At feeding they seem confused. They show interest when feeding but never eat. They just swim around. That last for 1-2 days after that they no longer come out to eat and just hide. They never show any signs visually their is a problem. I dosed medication for parasites for 5 days but lost the powder brown during dosing. She showed signs the 2nd day of dosing medication. Any thoughts?

Thanks
Ed

 

[snorvich]

Sounds like velvet. Best treatment is chloroquine phosphate in a hospital tank. What did you treat with?