You can’t top-up with non-RODI water like treated tap water because it causes a mineral buildup where the water becomes hard and polluted, this raises your GH, KH and PH to dangerous levels which will kill your shrimp, don’t do top ups do a weekly 25% water change and if you see you’ve lost a lot of water to evaporation do a larger water change that’s up to 50% of the tanks water volume and refill it to where you want the waterline, also is your soil a PH buffering soil? If so then it will kill neocaridina (cherry shrimp, orange shrimp etc) as it will make the PH acidic and KH too low for them.
The topping off might be the issue. Have you done any proper water changes since you got them? Unless you are topping off with RO water, the minerals in treated tap water will build over time inside your fish tank. This change in pH, kH, gH, etc can kill your shrimp. Either you need to change water every week, or top it off with RO. Otherwise, I noticed my shrimps health greatly improve once I added cuttlefish bone to my tank, just a small chunk. You can also use baked egg shells if you can’t find cuttle bone.
Probably from adding extra minerals on top of the minerals in the water you use to top off. It should just be RO water since all of the minerals are still in the tank after evaporation.
PM_Me_Your_Diseases 
If you saw planaria, it’s probably planaria. Also might want to test for copper.
You can’t top-up with non-RODI water like treated tap water because it causes a mineral buildup where the water becomes hard and polluted, this raises your GH, KH and PH to dangerous levels which will kill your shrimp, don’t do top ups do a weekly 25% water change and if you see you’ve lost a lot of water to evaporation do a larger water change that’s up to 50% of the tanks water volume and refill it to where you want the waterline, also is your soil a PH buffering soil? If so then it will kill neocaridina (cherry shrimp, orange shrimp etc) as it will make the PH acidic and KH too low for them.
Water parameters?
The topping off might be the issue. Have you done any proper water changes since you got them? Unless you are topping off with RO water, the minerals in treated tap water will build over time inside your fish tank. This change in pH, kH, gH, etc can kill your shrimp. Either you need to change water every week, or top it off with RO. Otherwise, I noticed my shrimps health greatly improve once I added cuttlefish bone to my tank, just a small chunk. You can also use baked egg shells if you can’t find cuttle bone.
You shouldn’t remineralise top off water only water change water.
Top off is to refill after evaporation, where no minerals left the tank.
Yah if your topping off with tap AND adding shrimp minerals you should probably do a kh/gh test, you may have liquid rock at this point.
If you don’t have the api kh/gh test you should pick one up, they’re only like $12 or so
Probably from adding extra minerals on top of the minerals in the water you use to top off. It should just be RO water since all of the minerals are still in the tank after evaporation.
You’d have to do a lot of top offs with mineralized water to kill shrimp in numbers like that. Methinks something else might be at play.
Are you topping off with treated water or straight tap?
Thank you all for the insight! Sounds like me adding the extra minerals when topping off might be the cause. Ill be making some adjustments