Sick infected Betta, what is best course of treatment?

Colin_T said:

It doesn't look like fin rot and the white patch looks like something has popped out of the fish.

Any chance of some more pictures?

If you can put the fish in the bigger container and do a 75% water change and gravel clean the substrate 2 or 3 times a week for 2 weeks.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Add 2 heaped tablespoons of rock salt (aquarium salt) for every 20 litres (5 gallons) of tank water. Keep the salt in there for 2 weeks then stop using it.
When you do the water changes during salt treatment, add salt to the new water before adding it to the aquarium so the salt level remains stable.

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Colin_T said:

If salt hasn't helped after a couple of days, then you might need a broad spectrum or an anti-fungal treatment.

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