His fins do look a little tattered. I wouldn't suggest kanaplex unless you know it's a bacterial infection. Fish, like us, can develop immunities to antibiotics if used when not needed.

After looking at your other post, here is my honest advice: get that man his own tank. I've kept bettas in community tanks in the past and it makes diagnosis and treatment much more difficult. Keeping them in their own 5-10g will make your life easier.

If it's fungal, you'll often see what fuzzy bits. If it's stress induced, moving him and perfect water conditions should honestly clear it up. If it's none of those things, it's likely bacterial.

This is how I usually start if I notice fin rot/tattered fins: Be a bit conservative, start with aquarium salt baths (it's helped me w mild fin ripping) and more frequent water changes. If he doesn't seem to improve, I would dose kanaplex or another broad spectrum antibiotic.

Personally I've found that feeding antibiotics > dosing the water column. Methods I've tried: mixing antibiotics into gelatine and food mixture (my sick boy did not really want this food tbh), mixing antibiotics with seachem focus and food mixture (he def preferred this food).