There are a few things you can try:
Substrate:
-Cypress Mulch
- Coco Husk
Both of these retain humidity really well
Tank screen:
- Cover 80-90% of the lid with tin foil, damp towel, or plexiglass.
Inside the tank:
- Use a larger water dish (surface area = water evaporation)
- Move the water dish to the hot side of the tank
- Good old fashion misting with a spray bottle
-Use a humid hide if everything else fails. (Get a plastic tupperware and put some damp moss or paper towel inside. Cut a little hole in the lid so the snake can go in and out as it wants. The humid hide provides a 'humid spot' rather than trying to make the entire tank humid.
Heat lamps suck up humidity like a sponge. So if possible, I would try getting the belly and ambient temps up so you don't have to use a lamp.
The red scale could be really minor scale rot. Don't worry too much about it if your husbandry is good. It will go away with the next shed or two.
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