First off, sorry to hear about the lost venustus, is the surviving fish eating yet?
I feel the need to chime in here since the thread referenced before was actually my thread.
In regards to NYA being a fluke ridden establishment... Even though I lost two Venustus from there, I would not say that I believe it to be from Flukes. FWIW, I have a small regal that I got from there at the same time and I don't recal that it displayed signs of flukes nor produced flukes during a FW dip and it is currently healthy as an ox.
It is my opinion that venustus are notoriously bad shippers and overly sensitive to ammonia poisoning. I plan to order Venustus again, and when I do, I have every intention of treating the acclimation vessel with an ammonia neutralizing product such as prime and adding methylene blue to help counteract any potential ammonia burning of the gills.
Having said that, when I do order a Venustus again, it won't be from NYA. I think the fish in his store are probably fine and healthy, (though i've never been there), but based on my experience in the past, I think a fish that needs extraordinary shipping precautions are best left purchased from DD. The packaging of the few fish that I have ordered from DD surpasssed the ones purchased from NYA by leaps and bounds.
Not saying his livestock is bad or that he doesn't know how to ship fish, rather that when it comes to the ultra sensitive and finicky species, I'll spend the extra $50 bucks and get it from Kevin.
Now back to the surviving Venustus.
I would agree with the water change and I would also continue to limit the light exposure for some time.
Have you given us any details about the quarantine system? Is the biological filtration pretty strong? Is there good flow in the tank? I have seen feeding responses from increasing or decreasing flow on certain fish.
Hopefully he starts eating soon, I assume the current foods being offered include brine and finely minced mysis. You might try live black worms if they are available, I hear they work wonders.
Good Luck!