Switching to aspen should help. Also sometimes those accurites are a bit off on humidity levels. If the sensor gets wet or is sitting right on top of the substrate it will quite often show the humidity level being much higher than it actually is. But 68% humidity is not terrible you just don't want it to stay at that level for too long. Sometimes too when you first put in new substrate, especially if you are using cypress it takes a little while for the moisture that is in the substrate to dissipate which will cause temporarily high humidity levels.