Bettas and fin rot

Question
I was watching my fish this afternoon and I noticed that my crowntail's fins are looking tattered. It almost looks like he was in a fight, poor Jess. It got me intrigued and worried, so I googled for Betta diseases and I found fin rot, which I think Jess has. I examined him carefully and the edges do look blackened, which convinced me it's fin rot.
Now for our facts (and I apologize in advance for making you cringe as a seasoned Betta owner/breeder/lover):
- this is our first experience with Betta (or any kind of fish, for that matter)
- we have two Betta, a crowntail (Jess) and a veiltail (Teal'c)
- we bought them at Petco, three months ago
- our tank is only a 2.5 gallon, with a divider (marketed for keeping two Betta, which I now understand to be a bunch of malarkey since Betta apparently need a lot more room than that)
- Teal'c, the veiltail, seems to be completely unaffected by whatever is messing with Jess's fins, his fins look perfect and he looks bigger, brighter and just thriving in general
- from reading your responses to other people, I think I need to change the water more often, however the tank does have a filter and we do use a Betta bowl conditioner
- we try to regulate the temperature in the room where we have the tank as much as possible and we have a thermometer to monitor the temperature, but I'm absolutely positive it does not stay at or around 82 degrees at all times; I don't know what can be done about this, though, considering how small our tank is, are there even good heaters that would be appropriate for a 2.5gal tank?

My questions to you are...
Even though I am convinced it is fin rot, how can it be that Teal'c is not affected at all, if it's being caused by poor water quality? Maybe he just hasn't gotten it yet?
Also, considering I have a two-fish tank, do you think I should start with the aquarium salt baths? And see how Jess does with those? How fast can I expect results, or improvement, at least? If Jess doesn't seem to respond to the baths, where should I go from there?

I hope I didn't forget any details that might help you.
I appreciate you taking the time to read this, and thank you in advance for the help!
Cristina

Answer
Cristina,
Yes, I have cringed. 2.5 gallons is the absolute minimum size tank for one Betta and definitely not big enough for two. You can get a plastic tank called a Critter Carrier that would be a lot better than what they are in and they are very reasonable in price. There is no heater that will keep the water at 80-82 degrees in that small of a tank. If one Betta has fin rot, chances are the other will get it too. Weekly water changes are very important and more so when they are in a small home. Veiltails in particular need the larger tank because of their long slowing tail. Fish love to swim, and they need to, to remain healthy. The larger the tank, the easier it is to take care of. You can add some dissolves aquarium salt to their water at the ratio if 1 teaspoon per 1 gallon of water. Make sure you dissolve the salt before you add it to the water or you will burn them. You can do salt baths for the one that has fin rot. Make sure you use fresh salt water every time, and only let him swim in that water for about 5-7 minutes. Stay with him the whole time he is in the bath so that you can remove him right away if he starts to have problems.

Unfortunately, you will continue to have problems with them if they stay in that tank and do not have heaters. The best thing you can do is separate them, put them each in a larger tank and add a heater to both tanks.