What is wrong with my betta and how do I treat it?

Question
I have a betta fish that appears to have fin rot. I have tried both just basic water changes with aquarium salt and maracyn 2 with no prevail. Half his back tail has now been eaten away however it is oddly evenly eaten away and only seems to be affecting his tail and no other fins. His body itself seems normal. His activity level is high. Almost always swimming and still eats. I have now recently noticed though that when he swims its consistently against the side of the tank as if he is itching himself. He is kept in a 2.5 gallon tank that is heated with no filtration. He also gets fed 2 pellets a day and has at minimum of once a week water changes. Do you know what is wrong with him and the best way to go about treat it? He is our first fish and we are very confused because we have been trying to treat this for a month with no improvement at all. His back tail was mildly ragged at the time we purchased him so we believe this to be an illness he got from the condition at the pet store.

Answer
Kristine,
If he is "scratching" himself, then he has external parasites. Sometimes you can see them and often you cannot. When I have a fish that is doing that, I put that fish into a salt bath. You do this by dissolving 1 teaspoon of aquarium salt in 1 gallon of water. Make sure the water is the same temperature as the water in his tank, which has to be 82 degrees. Let him swim in the salt water for 10 minutes. Make sure you stay with him so that if there is a problem you can remove him right away. Do this twice a day making sure to use fresh salt water each time. I never use medication with my fish, so I do not know what medications work. I know Jungle make a product that I am told works good. Before you use any medication, make sure you know exactly what the problem is. Try the salt bath first and let me know how things are going in a couple of days.