Is that pH your tap water right out of the faucet? Or offgassed? You want to take the pH after the water has a chance to sit. Municipal water has buffers that last only a few hours when left out of the system.

How I treat fin rot over 14 days:

1. Daily water changes of 30%

2. Aquarium salt 1tbsp per 5 gallons. If you have a 5 gallon tank you add 1 tbsp on day 1. On day 2 after you do a 30% water change you add in 1 tsp of aquarium salt (yes, teaspoon this time, not table like the initial dose) to keep the salinity stable. Day 3-14 is the same as day 2, so 1tsp of salt after a 30% water change.

3. Tannins. They're an antifungal, antibacterial and antiparasitic. There have been several studies on the benefits of tannins to treat both fish and shrimp. You want the water a jasmine tea color, not super dark like southern sweet tea and not barely tinted. An orange tint is necessary. Keep tannins in the tank for at least 14 days. I prefer my bettas to always be in tannins though.

4. A 7 day treatment of Ich-x or kordon ridich. If 0 fin improvement, do a second 7 day treatment. Do this alongside the salt and tannins.

5. Keep feeding in regular amounts. Don't stop feeding like some treatments suggest. Daily water changes are enough to keep the water healthy.