Having a very bad day. I'm not sure what happened. I have a 45 gal FO /w 45lb of live rock. This tank has been running w/o problems since 2001. I have always used Instant Ocean salt. Saturday I made up a 10 gal batch like I do monthly only with new box of salt. I had the water temp at 80, salinity at .021, aerated for 24 hours. Monday AM I siphoned off 9 gal and added the new water. Turned one of the aerators up on one of the circulation pumps and watched everything for 10 min. Everything appeared fine. I went outside and came back in 1 hour later and every fish is DEAD!
I keep my mixing pails clean and are not used for anything else EVER! I did a water test for what I could. PH normal, Nitrates 0, Nitrites 0, ammonia 0. I am both devastated and lost as to what could have done this. The only thing I changed was the water. I find it hard to believe the salt was bad but I did nothing else but change the filters in the filter like I have every other time. I have been doing this same routine for the last 5 years and these fish have all been in the tank for that time. Any advice welcome.
I can not trace back any contamination. I'm lost.

I keep my mixing pails clean and are not used for anything else EVER! I did a water test for what I could. PH normal, Nitrates 0, Nitrites 0, ammonia 0. I am both devastated and lost as to what could have done this. The only thing I changed was the water. I find it hard to believe the salt was bad but I did nothing else but change the filters in the filter like I have every other time. I have been doing this same routine for the last 5 years and these fish have all been in the tank for that time. Any advice welcome.
I can not trace back any contamination. I'm lost.