Reptile & Amphibian Forums

Hi all

Recently I realized that my hygrometer in my pythons cage was a little off. So I bought another. I also have a digital one but its too big for the enclosure.

I tested to see which one is not working properly by placing them beside each other next to where the house thermostat is, watching the difference in humidity readings and comparing them to the house hygrometer. Whichever was not in line with the others is the faulty one right?

I was stunned to find that all of my hygrometers ( 4 in total) are giving me widly different readings. The house thermostat (also digital) says 40%, the digital one says 30%, one dial hygrometer says 20% and 2 other dial hygrometers say 55-60%!

The dial hygrometers are from exoterra and I'm not sure if they can be trusted.

How can all my hygrometers and my house thermostat be giving me seperate readings? Is there something about humidity physics I'm not aware of here or are all my meters busted?

(before you ask, my house thermostat's probe is where I tested all the equipment to make sure the playing field was even)

thanks all!

You have found what I believe to be the most common reason for people thinking they have lower or higher cage humidity than they really do. Low cost hygrometers are notoriously inaccurate and many can easily be off by 10% to 20% 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. I posted this earlier on this forum, but below is the procedure for checking humidity gauges or hygrometers:

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 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 some air inside as well, or a clear plastic food storage container is even better as long as it seals airtight.

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. The water and salt mix will reach an equilibrium humidity of 75% within any small airtight container.

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 have found that this is a very accurate way to check humidity gauges. Below is a photo of that hygrometer. I purchased it about 30 years ago and it rarely ever needs adjustment when tested. I believe it to be one of the best available for the money.

Kelly

Thanks for the info!

Very useful.

I tried it out and my digital hygrometer says 71-72% which is fairly close. it does not have an adjuster or anything but I can at least do the math whenever needed.

This helped a lot!

RDM