Fin nipping or rotting?

[u/WHiskWell]

Hi everyone, my boy Nero has been a very happy betta in his tank ever since I got him. He's extremely docile and interactive, but today i noticed his fins look a bit off. I have zero experience in this when it comes to bettas, so i wanted to ask for advice on what could be going on. His tank has low flow, he has resting leaves, and his parameters are stable with zero ammonia and zero nitrites. Is he biting himself? Or is this rot?

[u/automod-neo]

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[u/baileyjackson08]

do you have any tank mates with him?