I am on a well with a high sulfur content. I recently replaced my chlorine system and put in a sulfur block system It works great for the sulfur. I discovered that he smell came back and turned off my softener which caused the smell to go away. It was suggested that I ad chlorine to the salt reservoir and recharge the softener. I did this and ha chlorine smelling water for 2 days. When the chlorine went away the water took on a fishy smell. Turning off the softener makes the smell go away so I know the source is the softener. The softener is 5 years old, Any suggestions?

Turning off the softener makes the smell go away
This tells me the resin might be the smelly culprit. Try flushing with chlorine and if that doesn't fix the smell replace the resin. Good luck, Tom