Question about humidity

[TPring]

Is there an optimal/acceptable range for humidity [in relation to coins]? I am assuming less is better.


I keep my better coins in a safe and in that safe is an electronic hygrometer [to measure the air moisture] and, upon opening the safe, it usually reads in the mid-to-upper 50's [55-58].


I have three different methods of trying to reduce the moisture: an electric element (that came with the safe), moisture-absorbing beads and, a bowl of rice. However, I have noticed on a few occasions where the sensor reading actually dropped a couple of points after opening the safe.


Any suggestions/comments?


Thanks,