Finishing fin rot treatment??

Background info up top questions numbered out on the bottom:
On may 1st I noticed my betta Cloud had some behavioral changes which prompted me to take a closer look. Upon closer inspection I made a novice diagnosis of fin rot based on fin degradation and blackened parts of the fin. I decided to go for the least intense treatment because his degradation wasn’t very noticeable however it definitely worked its way down the fin a bit which also seemed to indicate fin rot.
I didn’t have a quarantine tank at the time so I opted to treat in Clouds 8 gallon tank. Because this is his main tank and i didn’t want to kill all my BB so I opted for 70% water changes and aquarium salt(one tablespoon per change), catappa leaves, and stress coat.
This is how I proceeded for a week and I noticed quite an improvement. I had read into stress being a main cause of fin rot and at the one week point I chose to do a 70% with the same amount of salt every other day so he could rest a little more easy. His condition continued to improve.
Now it’s my understanding that exposing bettas to aquarium salt for longer than two weeks can cause kidney and liver damage. So yesterday(day 10 of treatment) I did the 70 percent water change only no aquarium salt added. I did this to gradually taper him off hopefully causing less stress in the process.
This brings me to my questions:
I am planning on letting his water be through tomorrow and then one more 70% change.
1. After the next 70% change I plan to go back to the usual 25% WC every 10 days. Would the two large changes without salt sufficiently remove salt from the water and prevent organ damage?
2. He is looking and acting much better but the part of his fin that blackened and degraded is still there. It has shrunken/ shriveled up a bit doesn’t seem to bother him at all. Will his fin always be like this or should the degraded part have fallen off or completely gone away to consider him cured?
3. I will attach photos to show before and after. If he still has active fin rot my plan of action is to use erythromycin because the blackened indicates bacterial infection. Is this a good plan?
1st pic is when I first noticed. 2nd is one week into treatment. 3rd is today.
the fin rot is on the bottom end of his dorsal fin

 

I would still do the 25% changes every 3-4 days instead of every 10 to help keep fin rot coming back on real strong. The big water changes should get the salt down to very minimal levels, yes.

 

I would still do the 25% changes every 3-4 days instead of every 10 to help keep fin rot coming back on real strong. The big water changes should get the salt down to very minimal levels, yes.

Thanks will do will that part eventually fall off or will he always have that shriveled section of fin??

 

Thanks will do will that part eventually fall off or will he always have that shriveled section of fin??

It should heal eventually, just may take longer and part of why i suggested the frequency on the changes. Seems like that was probably the part most affected.

 

It should heal eventually, just may take longer and part of why i suggested the frequency on the changes. Seems like that was probably the part most affected.

Yea thats what stood out to me. Thanks for clearing that up I’ll keep a close eye to make sure his fin rot doesn’t rebound