Got all my russians as adults and I've never worried about humidity. Their shells are wonderful (but i lived in iowa where it is humid). How much humidity do the russians need?
I believe the first few years are the formative years . If you have adults your need has diminished .....now that they are adults.....this is my opinion.....I do not keep these awesome species so it is always a good thing to wait around to gather others opinions....
I'm not an expert on Russians, but if youo look at where they originate I'd say that they don't have a particularly high humidity in the wild. I'd continue not to worry!