If the RH ever got to 50% in my darkroom I would be adding to it with perspiration. It is usually in the 20-30% range, but can get down to 10% or less in certain weather conditions.

I normally do not re-humidify, but when the RH is extremely low, I do so over a small electric skillet with water almost simmering. Of course this also raises the RH in the general room atmosphere.