Why do you have that moss in a first place? And what kind of hydrometer are you using? Some are very crappy, as well sometimes when the sensor get wet it will read humidity at 99% even though it is way lower.

at any rate you need to fix environment, moss out, water dish out, the one in a big tank where nobody lives, increase ventilation, or you are risking to run into big problems with frogs soon enough. But too much humidity is easier to fix then not enough

Try to keep humidity at about 76%, then when it is a bit higher it still won't go over 80.