Dying fish

[Andy1968]

Hi everyone can anyone help me. I had my neon tetras over a year and today I added guppies and my tetras al died.
What could the problem have been?

 

[SayonROY]

Very sorry to hear that. Tank size? Neon tetras are easily stressed out that's why everything with them should go slow. but still all died! How many you had? & how many gupies you added?