Welcome to TPT. Can you tell us if there were any other changes recently, such as new plants added, work on the filter, other water or foods added/changed?
Decomposing organic matter (such as the soil in the plant pots) can cause anaerobic conditions, fouling water.
Things to consider: did you somehow knock out your biological filtration capacity (ability to take out nitrogenous waste) by cleaning or killing off the filter media?
Did you add any plants that may have had toxic treatments? Water treatments? Medications?
Do you overfeed, causing a nitrogen spike?
Has your water quality changed, such as your municipality adding new treatments to the water that are toxic to shrimp? Do you use tap, and do you pre-treat it with water conditioners?
Did you have a heater malfunction? CO2 overdose? Shift in pH?
The other possibility is the ghost shrimp came in with some disease that took a while to knock out the others, although the recent addition of them and their very fast death suggests some other toxic or deficiency death. It is within the realm of possibility that there is something toxic enough to knock out shrimp that is not toxic enough to affect the snails or fish.
What are all your water parameters: pH, GH, KH, TDS, nitrates, temp - any changes to any of them?
How is the filter set up?
We need more specific information to suggest etiology of shrimpicide. :biggrin: