So, I realized its a lot harder to observe your fish's health in a tub while only being able to look down on them. I noticed in the last couple of days, the naso tang barely has an interest in food and basically the whole fish population just lackadaisically eats and does not attack the food with gusto as usual.
When I had my 30 gallons of new saltwater ready to conduct a water change for nutrient removal purposes, I stared at the fish and started noticing that my tangs looked really thin. A closer inspection showed that they were definitely not eating as much lately and have gotten a tad thinner from it. I sat there and tried to think of why that could be... I know chloroquine phosphate does have some reports of it being an appetite suppressant. It also tastes awful to fish so perhaps they just got tired of their food soaking in the non-tasty CP tub water. The main fish population had been in the CP treatment since the middle of January... perhaps the extended duration of the treatment caused them to lose their appetite.
Either case, I thought it more prudent to stop the CP treatment at this time, especially with the known infected original population being treated for velvet for almost 1.5 months now (treatment period for velvet is 21 days in CP), I was probably safe from velvet and the more pressing concern was the lack of appetite of the fish.
I did a full water change to remove all medications in the tank, even the prophylactic prazipro treatment for intestinal worms and flukes. The goal was to remove all medications and hopefully restore the feeding responses from the fish. I also added activated carbon to assist in removing any residual medication in the tub.
I'll test their feeding response tomorrow afternoon... probably soak the food in selcon and garlic to entice them a bit. No tang can resist a nice garlic soaked sheet of nori!