Betta fish fins frayed

[Trin_h]

Hi everyone, I just need some advice for my betta fish and treatment

I left my house for 5 hours and my betta fish was going perfectly fine. When I got home, I realized his fins were damaged badly. It looks like its frayed. I have a feeling it might be from an ornament but I'm not sure and I want to find a way to prevent it again.

I did a ~30% water change today to the 5.5 gallon tank (I do water changes weekly). All the chemicals, ph and temperature was good. I didnt add anything new into the tank recently either. I got him less than 2 months ago and everything was fine before this. My betta fish also has this tank all to his own so the problem is not with other fish nipping.

I'll link pictures to him before I left and when I came back.

 

[SaraB]

Sometimes bettas are able to nip their own tails (because they are bred to be long). Not sure what could be causing it. Most theories include boredom or stress.
How long are your lights on a day?
What are your exact readings on your water test? Ammonia, nitrates and nitrites?
What is the temperature?