The instigating fish for this order was a medium Klein's butterflyfish for a friend to try to eliminate aiptasia (knowing the inherent risk with any butterflyfish in a reef tank!), and, of course, that was the fish that seemed to be in the worst condition when they arrived. Whether it actually helps or not, I "dip" my fish for about 15 minutes in a small holding container with HydroPlex after acclimation but before adding them to my QT. So far, I have never had troubles with this and all fish have acclimated well through even the 1/2-gallon container with HydroPlex.
Not today, though, as the Kleini gave me a scare when it went completely stiff on the bottom of the container after about 10 minutes, which prompted me to cut the time a bit shorter and add the fish to the QT immediately. It took a couple minutes for the Kleini to recover in the QT... from past experience with weird deaths of butterflyfish, this had me very concerned and I am quite happy that it seems to be healthy and back to normal now.
Looking forward to more pictures of your pony tank as it progresses! It looks to be a wonderful start so far.