It depends on your ambient air temp. What few understand is the relative humidity is relative to temperature and is a % of the saturation point of the air. That like dissolving sugar in water changes with temperature.

68% could be too low if your ambient air temps are below 77ºF. Or basically spot on 77-79ºF and slightly over 80-82ºF or quite a lot over beyond 82+ºF.

The other thing to keep in mind is the accuracy of hygrometers is often quite poor. Some of the digitals on the market are only spec'd at +/- 8% meaning if it reads 60% it could actually be 68% or 52%. Cheap digital units are highly sensitive to dirt (expensive units are very fragile and very expensive). They use a carbon pad and measure mirco changes in current this can be effected by any dirt or worse uranate or urnate dust. Anything that could change the electrical resistance. They are very frail. When I used digital units I replaced them once a year and tested them using a test kit (salt tests destroy digital units) every 6 months. I have never had a digital unit stay reasonably accurate (probe inside an enclosure) for longer than 12 months. I started to use good quality analogue units (metal body, glass face, calibratable, and METAL face cards) they have stood up better to the tough environment of the snakes enclosures. The units that actually have hair in them are too fragile as well. I calibrate them still once every 6 months (using a standard salt test) and after 5 years have yet to need to replace one. I rarely find the accuracy off by more than 3%as good or better than every digital unit I ever owned.