Scake rot takes time to develop so give us some history. How long has it been in the tub and how damp is the substrate? What substrate are you using? How often are you cleaning the tub and how is the airflow?
We need to see pictures of the tub and how the heat pad is setup with a thermostat. It must have the probe in physical contact with the heat pad on the outside of the tub. The temp must be measured from the bottom of the tub and not on top of the substrate.
You say the heat pad is 91 degrees. Is that the temperature the thermostat is set to or what you are measuring? Where are you taking temps at?
You say humidity is 70-75% but what are you using to measure it? That percent is slightly high to keep constant and we need to know what you do to keep that percent. If the substrate is too damp and kept so long damp that microorganisms are growing that can cause scale rot and the snake is in subpar conditions where the scales are compromised and there is an infection then improving conditions are far more beneficial than antibiotic ointment and betadine.
If you do have scale rot to the point where it is causing physical issues you need to see a vet to make sure the snake is not immuno compromised and to figure out what type of infection is causing rot.
Antibiotic cream for example will do nothing if it is fungal and betadine will do even less if there is no open wound.
Before you go to a vet, give more information and pictures of the tub setup.
Also answer Sauzo's question about the last time it shed.