Update on my situation:
That sick shrimp has been in quarantine for almost a week. At first I did nothing but put a little oregano oil in the water. I don't have the number right now, but it was about half the concentration of what a dose of API melafix would have been. It is enough the give the water a minty smell. The shrimp started to look like it was getting worse, so I switched over to fish antibiotic (doxycycline). It has been getting the standard aquarium dose, and the condition of that guy seems to have "stabilized", although not really getting any better. Still pink-colored and very inactive and doesn't really eat. But at least now it seems to just stand around looking bored instead of ready to die. It's had the doxycyline for 4 days now and nothing really happened, so I wonder if it is really a bacterial infection after all? Since I read that it would make the antennae broken / crooked, but physically the guy looks fine, except pink. Maybe time to switch to a different antibiotic?
In related news, I still have the problem of shrimp being inactive in my tank. It seems the blue bolts and babies are all fine, but the Red Wine Panda shrimp take turns being inactive for a few days each. The only thing I have been doing is occasional H2O2 treatment and less food than usual. The last time I "did" anything to the tank was at the end of march with that Dr Tim's Waste away. I know people say that what you do to a tank can have an effects that lasts weeks, but come on...