HCA: Hermit Crab Association

I'm trying to get my heat and humidity right with my new tank. I bought a Zoo Med hygrometer/thermometer with the 2 little dials and also a digital National Geographic hygrometer/thermometer . My problem is the Zoo Med says my humidity is 71% and the N Geo digital says it is 88%. Big difference. I am confused at to weather it is to high or to low. Any ideas would be great!

Try calibrating the zoo med one. It may be off!


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Calibrate both! ANY hygrometer can be off right out of the package, and they can fail over time as well. Testing is the only way to make sure it's right. Here's how: http://www.hermitcrabassociation.com/ph ... 26&t=92540

Ok...Thank you! Is there anyone that you find is really good and accurate? What most people use?

Most people use the Accurite dual digital unit from Walmart (under $10), but it can still be wrong out of the package.

wodesorel wrote:Most people use the Accurite dual digital unit from Walmart (under $10), but it can still be wrong out of the package.

Too true! I'm on my second Acurite and both were off even after calibration, the first registering a baseline of 69 degrees and the current one 67 degrees. I don't worry as the tank's humidity is always in the mid- to high 90s anyway and the Acurite is accurate re crabitat temperature.

I was just hoping that when you buy something it gives the right information. I have no idea what my humidity is. I do have both in a sealed tight container with some salt for the night. Guess I will have an idea in the morning. This forum has saved me quite a few times since I got these little guys!

It's not that they make them poorly, it's that the shipping process jostles the springs inside and knock them out of alignment. No matter where or what you're buying, it's important to calibrate it as any drop or shake can be enough to throw off the sensor - sometimes a little, sometimes a lot. They are delicate instruments but since it's not usually life or death it doesn't make a big difference to people if they read wrong. Products made for humidors can be better, but even those say to calibrate to make sure. (Hygrometers made to monitor really expensive cigars.)

Can the digital ones be knocked out of alignment too? I didn't know that.


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The sensors can go bad. Mine loose a few percentage points for every year of use. I haven't taken one apart (really should have ) but there is something exposed that has to read the humidity levels. I'm not sure if it's a pad or a spring.

Ahh okay makes sense. For some weird reason I just assumed that they didn't. Lol oops! :p


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I never thought they would either! But by the time mine die (after 3-4 years of use) they're usually about 10% off from where they started.

Interesting, definitely good to know.


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Well after calibrating all night, Zoo Med is 5% under and Nat'l Geographic is 5% over. At least now I have an idea! Thx everyone for the help!