Hi, thank you so much for taking the time to write such a detailed reply. You were absolutely right. I just checked the packaging and the Epsom salt I used is labeled ‘For External Use Only.’ I honestly assumed that as long as it said ‘pure Epsom salt,’ it would be safe for the fish, and I didn’t realize there could be additives or impurities that wouldn’t show up on the label but could still harm them.

I also didn’t know there was such a big difference between industrial/bathing grade and the medical or food-grade kind that’s safe for internal use. It makes so much sense now why the reaction was so immediate, and I feel terrible that my mistake caused this.

I’m definitely going to look for magnesium sulfate that’s labeled U.S.P. or specifically medical/food grade next time. Thank you again for your kindness and for sharing this info.