The tank still hasn't gotten out of the slump yet despite 2 15% water changes and good air quality this last week. A few things I have noticed is that after a dose of Bacter AE, the shrimp become active for half a day or more, and similarly with a H2O2 dose. I also took out the Oxydator since it didn't seem to make much difference.
One of my original shrimp died (11 months with me plus a few beforehand), although it was starting to look old and decrepit anyway. Another one of the original shrimp seemed to have gotten sick for a week but then recovered? So definitely "something" happened, but I have no idea except for the recent bad air.
It seems that one more Shadow Panda / BKK also got the short antenna symptoms, although still active. The other one that already had it seems to have slowed down now.
Looking back at my notes, I think these SP / BKK never did well in this tank, so now I wonder if it is bacterial or even genetic. When I first set up this tank, I got a pair of BKK from one breeder, and they did fine but one suddenly died after 6 weeks with the only symptom being somewhat curly but not short antenna. Then about 4 months later, the other one died with the short antenna. Neither of them grew up larger than a small size. And now, starting about 2 months ago, my own BKK / SP, which were born in this tank and did fine for 7-8 months, have been going one by one. Of these, only 1 or 2 grew up to be a large size. (They are probably female). From the same batch of babies, the blue bolts are doing fine and have long antennae that are 1.5x body length.
I reinstalled the pH meter, and it reads about a half point higher than when the tank was new. (6.0 to 6.5 now) So lower pH is supposed to be more anti-bacterial, but I don't know at this point if only 0.5 makes that much of a difference. I might just end up dosing the entire tank with minocycline if this bacteria is endemic. Some people on another shrimp forum claim that it doesn't kill off the filter bacteria.
I've also been thinking of transferring another shrimp to the Amano tank. It depends if I want to have shrimp babies in that tank, and if I would be willing to risk the health of those shrimp. Don't want to mess up a good thing, ya know.