Betta Fish: Best course of treatment for Fins?

Hi all! I need some help deciding the best course of treatment for my Betta, Sake!

Two months ago I noticed a chunk of his back tail missing directly from the base, and not seeing any clear signs of rot on top or bottom fins, I assumed it was a freak accident.

Last month, I noticed his fins begin to deteriorate. I had to move and somewhere in the stress of it he lost the last bit of his back fin, also from the base and bleeding. His top and bottom fins also developed signs of rot fairly quickly.

I quickly got to the pet store and bought a hospital tank (I already had a heater and small filter extra at home) and some EM Erythromycin. When I got home and got him acclimated to the tank (I put cycled media in the filter, no carbon), I opened the box of EM to find it empty 😖. Turns out EM is a high theft item and someone stole the packets from all the boxes on the shelves, so my only option was refund and wait for more EM or exchange for Fin and Body. I opted to exchange so I could start treatment asap.

It’s been four days of me putting half a packet in after a 25-50% water change daily. I use stress coat to treat the water too. Today I put in a carbon filter and am letting the tank sort of reset in terms of meds, and will repeat treatment tomorrow.

Is there any suggestions of where to go from here? Is my course of treatment good? I have Klanaplex coming in, can I use it with Fin and Body or should I use Klanaplex instead of Fin and Body when it comes in? I feel so bad for my fish, I hope he pulls through!