It looks like the lump is a viral infection which could be a symptom of another disease. You have talked about seeing white under the discolored scales- this could be the main disease, i.e. fish fungus, ich or even anchor worm, and I think the discoloration is just due to the sickness. You need to examine your fish carefully to identify the exact disease. See description in this article to help you identify the disease. I have also suggested some medications in the article. Have you tried Bettafix Remedy? Try this as it cures almost all fish diseases. It is also a great water conditioner! See the link for the medication i.e. at 10. Velvet, and buy it if you use Amazon.
Betta Fish Diseases: Sick Betta Fish
Fin rot may also be caused by a fungal infection or another underlying disease that has caused a weakened immune system or stress. It’s possible for a betta fish to be suffering from more than one ailment at once.
Betta Fish Disease and Illness: Preventions, Causes, and Cures
Currently on the Board of the aquarium often see the topics on , many of which are deadly dangerous fungal diseases of betta fish, damage to the aquarium. Please share with your readers some information about this disease. Fungal infection is a common disease common in tropical fish. Because the spores of the fungus is found in the , these spores will enter and infect fish when the fish are stressed (stress), injury or disease. Poor water quality can cause increased fungal infections on fish in the tank.
Also treat secondary fungal infections