Betta Fish Fin For Help!! I

I'm very new to the fish hobby and have an idea of what I'm doing but would take all the help I can get. This is my twin tail half moon betta, Lieutenant Dan. The first picture is what he looks like now and the second picture was a few weeks after I got him. I'm not sure if it's fin rot or tail biting but here is his setup:
He is in a 5 gallon filtered tank with 3 ghost shrimp and a few real plants. He also has a heater that keeps the temperature between 78 and 76. I do weekly water changes like clockwork. Recently I did an aquarium salt treatment for about 5 days where I put him in a 1 gallon tank and used 1 tablespoon-1 and 1/2 tablespoons of aquarium salt. It did not seem to help but he was still very active and was eating normally. Two days ago I decided to put him back into his tank after testing the water. The parameters are pretty much perfect. (nitrate zero, ammonium zero, nitrites zero, pH 7.0) I'm not sure what else to try, he seems like he's in good spirits but his fins are gradually disappearing. any help would be greatly appreciated. Thank you!

 

That is fin rot, I suggest daily or every second day water changes. Try some Indian Almond Leafs to help stop infections. I Did %75 water changes daily with IAL and my rescue betta made it. Do not use salt as its harmful for them!

 

That is fin rot, I suggest daily or every second day water changes. Try some Indian Almond Leafs to help stop infections. I Did %75 water changes daily with IAL and my rescue betta made it. Do not use salt as its harmful for them!

Should I do 75% water changes in my five gallon or should I quarantine him in the 1 gallon again and do 75% water changes in that?

 

5 gallon

 

Should I do 75% water changes in my five gallon or should I quarantine him in the 1 gallon again and do 75% water changes in that?

Depends, If he is to stressed I wouldn't move him. if he is acting fine you could. But having a filter and heater can help speed up the process.

 

5 gallon

Okay thanks I'm going to try that with the IAL.

Depends, If he is to stressed I wouldn't move him. if he is acting fine you could. But having a filter and heater can help speed up the process.

He doesn't seem to get stressed easily from being moved but I'm going to do it in the 5gal. Thanks!