Today I was doing a water change (it had been about 2 weeks, I know that’s bad), so I did a 75-80% water change to try something differently. Since I was doing a water change that big, I decided to put my 3 guppies in another container. When I finished, and put them back, I noticed that one of my guppies ( tequila sunrise) had a split down his tail, it was so random because when I put him in the container, his tail was just fine. He previously also had tail rot but recovered, or I think he did. I’m not sure how to fix it, help!!