My daughter's Betta is suffering from fin rot, and I'm struggling to help.
The Betta started in a 2 gal filtered and heated tank and was fine for ~3 months with weekly ~50% water changes. When we saw signs of rot, we prepared a new 5 gal tank and moved him. He's been in the 5 gal for two weeks, and the fin rot has expanded disturbingly.
In the 5 gal tank, Ammonia and Nitrate are non-existent. The "natural" pH is slightly high (our local water is high) at ~7.6, so we bring it down with API fluid. Temperature is at 78 F. This aquarium has been set up for two weeks and he is the only fish in the tank.
The tank has silk plants and a single decoration within which he can hide. The tank has gravel.
The new tank has three stage filtration, a heater, and LED lights that are illuminated ~66% of the day.
We initially did 20% water changes daily in the 5 gal tank, siphoning from the bottom to clean the gravel.
We feed three flakes of Fluval Bug Bites daily.
Once in the larger tank, we initially tried aquarium salts for five days with no apparent effect (fin rot got worse).
Over the past week, we've administered Bettafix, which advises no water changes, so we've paused those.
So, we've tried moving him from what we feared was a contaminated tank (nothing but the fish went from the original tank to the 5 gal), treating him with aquarium salts, and now treating him with Bettafix. We've monitored Ammonia, NItrate, and pH and adjusted the pH. We've initially kept the temperature a little low (~76 F) in the hopes of keeping anything bad at bay and now increasing the temp to 78 F.
The fish seems happy, is making bubbles, and made a bubble nest, but his fin rot is progressing, and I'm not sure where to go from here.

The Betta started in a 2 gal filtered and heated tank and was fine for ~3 months with weekly ~50% water changes. When we saw signs of rot, we prepared a new 5 gal tank and moved him. He's been in the 5 gal for two weeks, and the fin rot has expanded disturbingly.
In the 5 gal tank, Ammonia and Nitrate are non-existent. The "natural" pH is slightly high (our local water is high) at ~7.6, so we bring it down with API fluid. Temperature is at 78 F. This aquarium has been set up for two weeks and he is the only fish in the tank.
The tank has silk plants and a single decoration within which he can hide. The tank has gravel.
The new tank has three stage filtration, a heater, and LED lights that are illuminated ~66% of the day.
We initially did 20% water changes daily in the 5 gal tank, siphoning from the bottom to clean the gravel.
We feed three flakes of Fluval Bug Bites daily.
Once in the larger tank, we initially tried aquarium salts for five days with no apparent effect (fin rot got worse).
Over the past week, we've administered Bettafix, which advises no water changes, so we've paused those.
So, we've tried moving him from what we feared was a contaminated tank (nothing but the fish went from the original tank to the 5 gal), treating him with aquarium salts, and now treating him with Bettafix. We've monitored Ammonia, NItrate, and pH and adjusted the pH. We've initially kept the temperature a little low (~76 F) in the hopes of keeping anything bad at bay and now increasing the temp to 78 F.
The fish seems happy, is making bubbles, and made a bubble nest, but his fin rot is progressing, and I'm not sure where to go from here.
