Fin rot / injured fins?

Hello! So I have a "new" betta I got around a few months ago. I got him from petco, hes a dumbo ear male and is purple with white fins on the side and his back fins were lined with white as well. This week I started to notice his fins looking tattered and torn so I naturally tested the water, which I will have posted, as well as pictures of him before and after. I keep him in a 20gal long tank with 3 ottos. There only decor is driftwood and big bundles of guppy grass that he loves to hide in. Nothing that could have really torn his fins. The water parameters look fine to me, I keep the tank at around 80 degrees. Im not sure how he got injured like this, but any advice would be greatly appreciated. Ive had a few bettas before and never had an issue with fin rot they all lived pretty healthy lives, but im always learning and appreciate any feedback. Also might want to include he seems to be acting active and normal besides the appearance of his rear fins. Sorry for the poor image quality, the first two is his after and as you compare it to the last photo, you can definitely tell the difference.