Fish Kill

[animal clubbers]

Earlier this week I changed 20% of the water in my aquarium. I used salt that I had had for a several years.
Within 4 days, all my fish died. They had all been hardy active fish and diedwithin hours of each other (on the 4th day). The chemisty is/was perfect.
Does salt go bad?

 

[marty]

By no means am I an expert in this, but here is my 2 cents!
Could the salt you used been contaminated somehow? How was it stored? Did it look clumpy and moist? How long did you let the newly made saltwater sit before adding it to the tank? What type of water did you use (and have you used this water before)?
Just some thoughts to see if there is anything else that could have happened....
HTH!