Betta has something?

Colin_T said:

It could be colouration, excess mucous or a minor wound.

Big (75%) daily water changes and gravel cleaning the substrate usually help.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use them. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens.

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The anti-biotics you used (Kanamycin) might have wiped out your filter bacteria so monitor the ammonia, nitrite and nitrate for a few weeks.

Anti-biotics should only be used for known bacterial infections that have not responded to normal medications/ treatments. Improper use and mis-use of anti-biotics has lead to drug resistant bacteria that kill people, birds, animals, reptiles and fish.

Please, try not to use anti-biotics unless you know the fish has a bacterial infection. These usually show up as red areas or red sores that grow/ spread rapidly. A white mouth that spread rapidly over the face and kills fish within 24-48 hours can also be a bacterial infection.

But normally if you do a big daily water change, gravel clean the substrate, and clean the filter, it will help most fish health issues, and at the very least buy you time to try and find out what the problem is before treating it.

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