Help with an HQ Rasbora!

[Moonstone]

Hello everyone! I'm Maria and Im new to the aquarium life but I'm very excited to become an expert! But since I'm new and not very good.
I recently purchased a small HQ Rasbora to add to my rasbora community. Everything was good until I saw this morning that the top half of his tail fin is gone! I'm almost certain I did NOT bring him home from the pet store like that. So I assumed it was bitten off by another fish, maybe the Serpae tetras I have? I have placed him in a hatchery box just in case it's fin rot and needs to be treated but I cannot tell if it's fin rot. But if it was BITTEN off, what should I do? How can I help? Any and all advise is welcomed!


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[StrangelyNormal]

Fin rot in my experience always had black edges. I'd keep him alone until it grows back, and test your water quality since fin rot is most often caused by poor water quality. Test your ammonia, nitrite, and nitrate. If ammonia is anything higher than 0 it's a problem.

If it's bitten off, you'd have to find out who's doing the biting, so I'd watch the other fish to see if anyone's a perpetrator.