As Martin said, 75% humidity is not necessarily bad. I always advise people to throw away their hygrometers, they are usually inaccurate to start with and will cause you (and the frogs) more stress than it is worth messing around trying to hit a number on the dial. I have kept red eyes at humidity levels ranging from 30% to nearly 100% depending on the season, setup of the particular viv, and conditions in the frog room. The key is good ventilation, except for very limited periods during breeding you should never cover the screen section of the top. As long as they have a water dish available to soak in at night they will be just fine, they are exposed to very dry conditions at some times in nature and have evolved to conserve water much better than we think they do.