Beta Fish has fin rot. Not sure what meds to give him?

My two year old red Beta named Fred has recently contracted a slight case of fin rot. I say "slight case" because its only on the edges on his top fin and alittle more progressed on his bottom fins. Its however very troublesome to me as he is my fish and I love him. I`ve had a few betas in the past and they never got sick and lived 4ish years. I am not one of those beta ppl who keep the fish in a teeny tiny 1 gallon tank. My fish lives all by himself in a 10 gallon, filtered and heated tank. I change 25% of the water each week and add the appropriate clorine and othe harmful tap water chemical removers, along with a waste control additive which cuts down waste. I also add "cycle" to promote the good bacteria to benefit the cycling of ammonia to nitrite and nitrate. The temp in the tank is kept at a constant 80 degrees. This is the first time this has ever happened to me with any fish as I try my greatest to take good care of them! He eats beta flake fish food. Lately he hasn`t been eating as much, I figured he must not be too hungry, I fed him alittle less the next day. He them seemed lazy. I figured he might be getting old. I studied him and noticed the beginnings of fin rot. He just isn`t himself and this pains me because I`m worried he`s in pain. I DID RESEARCH ON FIN ROT AND THE PICS ONLINE SEEM TO MATCH UP WITH HIS CONDITION! So now I am worried because all the website tell me to give him this or that med, but then others contridict the first website saying that this and that med isn`t effective. So now I am confused. I added two tablespoons of kosher salt to the water to help keep the fins clean. Now I just need advice on what meds to get him. Thanks.