[babydollkate22]

I was just changing my betta's water as I do on Saturdays, and I noticed that a large piece of his fin seems to be gone. As I inspected further, I'm noticing signs of what I suspect are fin rot. This is my first betta and I have only had him for about two months. I will post a picture in a comment from my phone in a couple of minutes. Can anyone confirm for me? I figured I would treat with salt (1 tsp/gallon, completing 100% water changes for 5 days or so until improvement is seen) as I read is recommended. Should I move him to a smaller one gallon bowl to do so? Here are my answers to the questions you recommended I cover:

Housing
What size is your tank? 4 gallon
What temperature is your tank? 79 degrees
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
What tank mates does your betta fish live with? no one else.. just the betta

Food
What type of food do you feed your betta fish? pellets
How often do you feed your betta fish? daily, six pellets. occasionally I will give him freeze dried blood worms as a "treat."

Maintenance
How often do you perform a water change? weekly or sooner if water conditions are unfavorable
What percentage of the water do you change when you perform a water change? 50%
What type of additives do you add to the water when you perform a water change? I add a tsp or so of Tetra Safe Start, and I treat the water with Tetra BettaSafe to condition the water. I also add a pinch of aquarium salt.

Water Parameters:
Have you tested your water? If so, what are the following parameters? I last tested it on Wednesday (it is now Saturday). I set up the tank a few weeks ago and used SafeStart, and I was consistently reading 0-0.25ppm in Ammonia, 0 in Nitrite, and 5-10ppm in Nitrate every day I tested it. I tested it daily after I first added SafeStart and for the first week after I started getting Nitrates to show up, and then every other day for another week, and now I check it once mid-week to make sure everything still seems okay. On Wednesday, the levels were as follows:

Ammonia: 0-0.25ppm (it's not quite that golden yellow color, but not quite as yellow-green as the 0.25)
Nitrite: 0ppm
Nitrate: 10ppm
pH: I don't test this regularly, but I know my tap water is at about 7.6.
Hardness:
Alkalinity:

Symptoms and Treatment
How has your betta fish's appearance changed? He is missing a large piece of his back fin, and his fins in general seem shorter and more ragged.
How has your betta fish's behavior changed? Not at all.
When did you start noticing the symptoms? Today
Have you started treating your fish? If so, how? No
Does your fish have any history of being ill? No
How old is your fish (approximately)? I got him as an adult from Petco in early July 2014.

 

[babydollkate22]

Some pics. Sorry they aren't better. He keeps coming to greet me and then I can't get a great view.

 

[MameJenny]

That looks more like tail biting to me. I have a chronic tail biter, and his fins usually look just like that. See how his fins seem to have U shaped cuts in them, and how there are ribbon-like strands? Those are the main indications that it's fin biting. If his tail has a black or red edge and seems to be receding, it's fin rot.

There isn't really a treatment for fin biting. Just keep his water clean and warm. The salt won't hurt, but it's not really needed. You should see clear regrowth within a few weeks.

 

[babydollkate22]

Some of the edges are kind of gray-ish, and a few of those ribbon like pieces look kind of frayed. It's hard to know for sure!

Is fin biting dangerous to him? I literally think he did it in like a day! I watch him for a while pretty daily, and yesterday was the first time I noticed it, and his fins are significantly shorter and damaged. :/

 

[BettaMummy87]

Try interacting with him a little more, one reason they fin nip is boredom! Taht or try rearranging the ornaments in his tank, or add a new one. Also, you can try placing different (brightly coloured) things outside the tank, like a toy or a magazine/pictures, and swap this item out. They like investigating and they're bright fish. If you're feeling really ambitious you could try 'training' him to do tricks.

The other reason is normally either stress or they think their fin is too big (common in older bettas, as it keeps growing, so once they're older it can become a bit of a hinderance with HMs and the bigger finned types).

Good luck!