Betta Fin Disease Diagnosis Needed

[vlwoodyard]

My betta recently developed this spot below its top fin as well as some darkening and has gotten worse recently. To the point where he seems unable to move the top fin.  I have done a full week on BettaFix hoping that would help but no improvement. I am clueless as I have never treated a sick fish so could use some advice. The only change has been I used to use bottled spring water as we have a water softener, but recently found a way to bypass it so have used the (hard) tap water after de-chlorinating it. I have made the change gradually with water changes. Water temp 78 degrees, 10 gallon heavily planted tank with heater, filter and only a few Cory catfish as tank mates. Photo of test strip attached is Aquarium Co-Op brand. Is the pH and GH too high with the new water? Any idea how I can help him? Thanks in advance!

[Colu]

Looks like the start of a tumor they are really common in Bettas  due to low genetic diversity it could be benign treatment wise there's not a lot I could recommend @vlwoodyard