The fish died 2 hours after introducing the snails?
What size tank? How many fish and what kinds?
How long has the Tank been established?
When did you add your last fish?
Do you use Co2? Excel?
Yes, and the rest of my tetras died overnight. Gouramis looking weak. 30 gal, 2 pearl gouramis and 8 glowlight tetras, established for almost a year, last fish added a few months ago. No co2/excel(mostly rock and wood). Invertebrates all doing fine though