u/GovernmentThink

Hello!
A few days ago, I noticed that one of the swordtails was clamping its fins. When I took a closer look, I saw that its scales seemed to be rubbed off. I then took her out and placed her in a quarantine tank with Esha 2000. I thought she might have gotten stuck between some rocks and injured herself there.
It’s now been a few days since starting the Esha treatment, and she is still in quarantine with Indian almond leaves. However, it now seems more like it’s getting worse instead of better.
That would mean she must have something else.
All the other swordtails and fish in the aquarium are fine. pH is 7, KH 5, GH 10, aquarium size around 500 liters. Any ideas what it could be?