One of the major factors in cage humidity regulation is what type of gauge you are using to measure it. Many hygrometers are notoriously inaccurate and can easily be off by 10% to 25% depending on the brand. Unless you are willing to spend 150 to 200 dollars for a NIST traceable with a certificate, you can never be sure if your hygrometer is reading accurately. However, you can test your own quite easily to see if it is reading properly, and here is the procedure:
1. Place a teaspoon of salt in a bottle cap or small cup and dampen it with a few drops of water (without dissolving it) to make it the consistency of wet sand.
2. Carefully place the wet salt and the hygrometer, or its probe if that type, inside a see-through container and close tightly. Don't allow any of the salt to directly contact the hygrometer. You can use a zip lock bag provided it seals good and you leave as much air as possible inside as well, or a plastic food storage container as long as it seals airtight. It may be better with the probe types to place the entire unit, probe and all, within the container so as to insure that everything is air tight.
3. Let it sit for at least 8 hours at room temperature and note the reading on the hygrometer without opening the container. It should read 75%, and the difference is how much your hygrometer is off.
4. If it does have an adjustment screw or other adjustment device, adjust to 75%, through a small hole made in the bag if necessary.
I have an expensive certified dial hygrometer I purchased many years ago and have checked it periodically using this method, and it shows to be a very accurate way to check hygrometers, as when done correctly, the humidity within the container or bag is always within a percent or two of 75%.
Bill makes a good point about humidity that is too high. As long as the humidity is not consistently above 85%, you shouldn’t have any bacterial issues as long as you keep the cage clean. Retics can tolerate pretty high humidity in a clean captive environment, and a higher humidity (70% to 80%) will help the RI recovery.
Kelly