Fin rot, tail biting, or a combination?

[tisburylane]

Well, I can't believe I'm making this post AGAIN.

Yesterday or the day before I noticed Finnick's anal fin looked very slightly frayed, just a little rough on the edges. I boiled it down to a bit of nipping.

Upon returning from class today, Finnick's caudal fin is frayed on the top half. There is the barest black edge on part of the top; if I hadn't been looking closely I wouldn't have seen it. His anal fin looks slightly more frayed, with a large rip about half way through. What worries me, though, is that there are two holes in his anal fin. I've heard this is a sign of fin rot. They are not like pin holes though, more like cuts. The edges of them do not appear discolored.

So I'll ask the same question as last time: Fin rot, tail biting/ran into something, or tail biting because he has fin rot?

Housing
What size is your tank? 1 gal
What temperature is your tank? 78-80
Does your tank have a filter? yes
Does your tank have an air stone or other type of aeration? no
Is your tank heated? yes? My heater is being suspicious.
What tank mates does your betta fish live with? no one

Food
What type of food do you feed your betta fish? pellets
How often do you feed your betta fish? 2 pellets twice a day

Maintenance
How often do you perform a water change? 2-3 times a week, although because of the water evaporating I may add 5-10% water in between then.
What percentage of the water do you change when you perform a water change? 25-50%
What type of additives do you add to the water when you perform a water change? StressCoat+. I applied a 1/2tsp of aq. salt a few weeks ago. Should I add more?

Water Parameters:
Have you tested your water? No, I lost the results sheet.

Symptoms and Treatment
How has your betta fish's appearance changed? Frayed tail, very slight black edge, holes in anal fin.
How has your betta fish's behavior changed? Not changed. Still excited to see me, still begs for food, happily swims around tank.
When did you start noticing the symptoms? Yesterday or day before for the anal fin fringe, the caudal tail fringe and black edge were this afternoon.
Have you started treating your fish? If so, how? 50% water change, first dose of TC Tetracycline.
Does your fish have any history of being ill? Fin nipping/possible fin rot around 2 months ago.
How old is your fish (approximately)? I got him around June. No clue otherwise.

In the second photo you can definitely see the fringe. Below the fringe, that lighter colored part is the part that is still healing from the last bout. It was what the fringed part used to look like.

[lvandert]

well in a one gallon, even with a filter, you'll need to be doing water changes day, preferably 25%-50%. As for his fins if they are just missing then its tail biting but if they have a black discoloration then I would treat with meds for fin rot. It's good he's still active it means it hasn't gotten really bad.