Betta Fish: My betta is fin nipping and I don’t know why?

This is Kairo, I've made a post or 2 on him before, my mom dumped him on me in September after I pointed out he had fin rot. Since then he got a lot better and looked much healthier. Though recently he's started fin nipping and I'm not sure why. (I know they're not the best pics, and I know I need more plants, I had to pull some out because they died and I couldn't save them)

He's in a 5g and there's nothing I'm the tank for him to rip his fins on. His only tankmates are 2 nerite snails (I know 2 nerite snails in a 5g isn't ideal, they were originally in 2 separate tanks). I had a couple ghost shrimp with him about a month ago but he ate them.

My parameters are currently ammonia and nitrite 0ppm, nitrate 5.0ppm, and pH 8.0

Any suggestions on how to stop his nipping/help him? I'm starting to give him salt and maracyn oxy baths, since that's how I originally healed his fin rot.