I change 80-90% of the water twice a week! And all parameters are good. He actually looks much better this morning. If I wasn't looking for it the injured area would not be noticeable. Maybe the peroxide treatments for 12 days straight was stressing him out. I don't know what to do anymore...At least he is not getting worse.
Ack! sorry I've not checked this thread sooner!
Fin rot is a pesky illness and it is totally normal for it to take a while to go away, whether using medications or natural means!
I once dealt with a case of fin rot that lasted for 3 weeks
straight no joke. I used the peroxide every day and was worried I would have to resort to stronger meds, but it did clear up eventually I just had to be patient. It was my favoritest fish ever Elsie Amber the l (she passed away when she jumped out of the tank one night) and it was agonizing to watch it linger for so long. Her case was soooo nasty the fin rot was more than 1/2 way up her tail. But I kept a concentration of salt in the water the whole time and did the peroxide treatments every single day and it did eventually go away. I was afraid, like you, of stressing her out by doing the treatments so frequently but it really was working to cure her fin rot. Some strains of it are just harder to fight.
If it is not getting any worse I would highly advise you not to use stronger medications! Those only stress out the fish even more because they impair can water quality. I would only use them if the fin rot begins to get aggressive and you are finding it to be worse and worse every day. But it sounds like it isn't getting worse, it is only taking a while to clear up. Give it a little time and try not to panic! I know it is hard when you see one of your "babies" struggling with an illness but keep the water pristine and keep doing what you're doing.
The fish has an immune system of its own remenber! They can pull through many things you would be surprised at. The peroxide is a disinfectant and if you keep seeing it bubbling it means it is working. Don't abandon the treatments just because you do not see visible improvement. Keep at it, and like I said if it really starts to get worse then you can use the meds you have on hand. Don't fret...the degree of fin rot your fish has, in my opinion, is not life threatening. Only when it gets out of hand can it really endanger your fish.