And if you have only GH additive, Neos won't care, I might add. I keep a few tanks of them at 0 KH and they do among the best of any of my shrimp tanks. I wouldn't do that if not using buffering soils, but that's another discussion. Bottom line is that carbonate hardness/pH doesn't seem to be all too crucial as long as they can make up for any missing minerals in their diet. The biggest ways I've messed up (and seen others online) is putting them into too recently set up tanks (which you haven't) and putting them through too much change in water chemistry. Even "good" changes have to be very gradual with these. Drip-acclimating them to your tank helps a ton, as does getting shrimp raised in parameters not too far off of your own water. I even drip my water changes to avoid any swings, and my change water is pretty darn close. Whenever I buy shrimp I pester the seller for their water breakdown if not provided. These are resilient little creatures to conditions FAR from what the care sheets suggest, but they do not suffer changes well. The fact that you are only losing a few at a time is encouraging, though I get that it may not seem that way. When you fluctuate a shrimp tank too much you often have no shrimp left. Only other advice I have is to barely feed them. If they aren't swarming your food, you should have skipped that day.
Nothing good happens fast in an ecosystem.