Nitrate 5-10 in one tank , then the other 0
Gh Is 300 range (off the chart on the api liquid test)
Water changes ~20% weekly
Substrate is plain old aquarium gravel
Feed a crumb every 3 days and remove uneaten food after two hrs.
Tank has been set up since October
Look's good to me unless shrimp are variety that need soft acidic condition's.
I keep cherry shrimp's and amano shrimp in water near identical.
No copper based med's,or algaecides used lately?
I might increase the temp a little bit.
I only say this cause I noticed my own tank's having a bit more trouble maintaining heat in single digit temps we have been having.
With light's on,,my water stay's around 75 degree's F but at night after light's out,,,,I can see red light on heater from across the room is staying on much longer indicating the heater is working harder.
I do hope it is not some type of pathogen.
If shrimp's are dying,,and no other life in the tank,,i might be tempted to just let the tank run for a few week's without shrimp.fishes,but feed the tank a bit of food as though fish/shrimp were present.
Not many pathogen's can exist for long without fishes/shrimp's to act as host's.