It's the potassium water softener! I tried and tried to keep shrimp months ago and everything else I could keep alive, fish, snails, ghost shrimp, but not the cute little cherries or any other shrimp. Not to wash my hands and call myself a shrimp murderer, I got every test I could think of and some suggested!
After almost giving up I dug as deep as I could and found everyone else who used potassium water softeners couldn't keep dwarf shrimp. Basically they'll swim around like they are drunk, and then keel over and die.
I now use a 90% mix of R/O water and 10% nonsoftened tap with a small bit of prime to add in minerals, and usually a drop of shrimp minerals. I now have tons of shrimp babies, and no more mysterous deaths.
Your water softener won't kill fish or plants, but will sadly continue to murder dwarf shrimp.
Back on the forum after two moves across two years! Slowly getting back into the hobby!