The first comment is the digital humidiy instruments are crude at best you might test this one to see if it is reading correctly. google 'salt test for hygrometers' pick one it is very simple. The second question is what is the humidity in the room? If your room is sitting at 80% you will not get it below that anyway.
humidity is not too much of an issue really 60 is an average for one region og the natural range other areas are higher and some lower. Hell areas of the sahara it is averaging 40% my point is high humidity isn't generally too much to worry about. High humidity and low air flow is but you don't have that issue Mr. Swiss Cheese (LOL). Just keep the tubs clean as bacteria grows well in moist warm places you might up the 'full cleans' to at least once a month (don't forget the top surface the 'cover' of each shelf) You might think on doing it a bit more. use your nose if it smells anything other than clean it is time to clean. Also before you replace the cyprus (or is it meluccia?) leave it out for a few days on a try in the sun to dry.