Have you tested your water quality? Is that the ph? If it is then that is perfect ph
Also dose the the tail look like it's been nipped or split, also can see any redness around it? It looks like it has been split. Cause the tear is about halfway down the tail
What other fish do u have? 3 sailfin mollies, 1 Cory catfish, 2 glass catfish, 1 kulih loach, guppies, zebra danios and 2 platys. Also 1 sailfin Molly died a couple of days ago
How long have you had the tank running? About 3-4 weeks
When did u last ad any fish? About 1 week ago. Which was the sailfin mollies and glass catfish
What filtration do u have running? I'm sorry I don't know what this means
thankyou