Humidity question

[Malum Argenteum]

I agree that Repti Chip is a great option. The snake should have a moisture gradient too, or at least some good choices. The snake should be able to choose its own temp (which you have, the heat lamp), but also choose the level of moisture in its immediate area. At absolute bare minimum it should have access to a moist hide. Better is both a moist hide and a dry hide in each the warm end and cool end of the cage (so the snake can be at any combination of temp and moisture level). It is easiest to provide a moisture gradient using a substrate like Repti Chip, and maybe tossing a little damp sphagnum under a couple of the hides too, and having those be in the moister areas. Snakes can burrow into the Repti Chip to find a really preferred set of conditions, too.

I'd recommend keeping an eye on the snake, and not doing anything too crazy to accurately target some RH number that some AI wrote on the internet (RH meters aren't very accurate, anyway, for reasons that have to do both with hardware and with user variation). I've bred nelsons and pueblan milksnakes (now both the same species -- L. polyzona -- but it looks cooler if I list them the old way ) and kept one hondo hybrid for a bunch of years (my first snake, actually; I had her for probably ten years and then she went to a local camp nature center), and breed costa rican blacks currently. They're all quite tolerant of a range of RH.