Calibrating a hygrometer

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Calibrating a hygrometer

Post by CrabbyLover77 » Sun Mar 22, 2020 10:37 pm

I got my new digital hygrometer today. I put it in a container next to a small lid of damp salt. To make sure it was air tight, I put that container into a gallon ziplock bag. It's been almost 8 hours now and is reading 67%. I know it says wait 6 hours on the HCA directions. I'm wondering if I should wait longer, until the % stops moving for at least 2-3 hours to determine if this hygrometer readings are off or not.
Thanks! I hope everyone is doing well!

Edit: It just went up to 68%, so it's still changing.

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Last edited by CrabbyLover77 on Sun Mar 22, 2020 10:37 pm, edited 1 time in total.
My Pets: 1 Pomeranian, 1 Russian tortoise, fishes/snails(40 gal freshwater aquarium), and 4 hermit crabs.
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Re: Calibrating a hygrometer

Post by Motörcrab » Mon Mar 23, 2020 5:28 am

I believe the 5-6 hours is a minimum time to properly calibrate. Waiting longer shouldn't change anything.

Be sure the sealed area isn't too big for the amount of moist salt you are using. Try and make the sealed area as small as possible. If you can't do that add more salt for the sealed area to make it work better. Similar to if you add a teaspoon of sugar to a cup of tea you would need more for a pot.
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Re: Calibrating a hygrometer

Post by CrabbyLover77 » Mon Mar 23, 2020 8:33 am

Thanks for your reply! Here's a pic of my setup. Do you think I used enough salt? The % did go up since I last wrote. It's up to 70% now. I was reading on a couple of online sites to leave it sit for at least 24 hours. I'm at 18 hours now. Thank you. ImageImage

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Re: Calibrating a hygrometer

Post by KimzKrabs » Mon Mar 23, 2020 9:18 am

I recently did the same thing however there was no way to adjust the % of the humidity after the calibration was done(I think it was done I left it for like 12 hours) so I’m really not sure it got calibrated. I also calibrated my timer for the fogger the same way and it reads about 5% difference sometimes higher sometimes lower. I’m finding this to be maddening lol . My temps seem to stay ok most of the time but since I’m home a lot it’s ok I can adjust as I need. If I was able to travel or go anywhere for any significant period of time I’m not confident the levels would stay ok and that’s really why I got a timer to begin with. I really love my crabbies and have become very attached and I’m always worried wondering if their ok.


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Re: Calibrating a hygrometer

Post by Motörcrab » Mon Mar 23, 2020 10:02 am

Once you get to the 24 hour point I would just figure out the difference between the two readings and adjust your humidity from there.

Kim it sounds like you will need to figure out the humidity variance on your gauge then the difference on your fogger and adjust to your gauge. I would still be very cautious with a fogger. I would really try to figure out why your humidity isn't right without it. It could be as easy as a different lid that seals better.

I always like to go a bit overkill with the UTH's. I found its a lot easier to cool a tank than warm it up. I just add a thermostat to the biggest UTH and allow that to regulate the temperature. All winter I managed to keep the temperature between 78-84 in the 75 gallon. I have an 11x47 UTH on the back and an 11x17 on one side. Both are insulated. If I turned the other UTH on I could have easily got the temperature to 86-88.
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Re: Calibrating a hygrometer

Post by KimzKrabs » Mon Mar 23, 2020 10:39 am

Could you send me a link to which heater you purchased? I have 2 on the back but heats no really the problem but maybe a different heater will help keeping humidity adjusted. I probably do need to get a different lid like plexiglass I suppose . Thank you for the reply


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Re: Calibrating a hygrometer

Post by Motörcrab » Mon Mar 23, 2020 11:29 am

I use Ultratherms from Reptile Basics. They have the best prices that I have found.
https://www.reptilebasics.com/ultratherm-heat-pads


This is the thermostat we use on all five of our tanks. We have been using these for probably two years with no issues.
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Re: Calibrating a hygrometer

Post by CrabbyLover77 » Mon Mar 23, 2020 11:33 am

Motörcrab wrote:Once you get to the 24 hour point I would just figure out the difference between the two readings and adjust your humidity from there.

Kim it sounds like you will need to figure out the humidity variance on your gauge then the difference on your fogger and adjust to your gauge. I would still be very cautious with a fogger. I would really try to figure out why your humidity isn't right without it. It could be as easy as a different lid that seals better.

I always like to go a bit overkill with the UTH's. I found its a lot easier to cool a tank than warm it up. I just add a thermostat to the biggest UTH and allow that to regulate the temperature. All winter I managed to keep the temperature between 78-84 in the 75 gallon. I have an 11x47 UTH on the back and an 11x17 on one side. Both are insulated. If I turned the other UTH on I could have easily got the temperature to 86-88.
Thanks Motor. I just checked and it's still at 70%. The description of the product says it's +/-3% RH. If mine stays at 70%, then it's off by 5%. The temp gauge seems to be ok on it. Would you return it if it were you and get something that's not so far off? Thanks!

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Re: Calibrating a hygrometer

Post by Motörcrab » Mon Mar 23, 2020 11:42 am

I would probably just keep it. If you are trying to keep 80% humidity you just need to remember to add 5 for 85%. If it drops below 80% you know your humidity is low.

For a while I was paranoid with humidity after a Zoo Med gauge stopped working. Our substrate got too dry and I dried out a molting crab. For a while we kept two gauges in our tank for double redundancy.

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Re: Calibrating a hygrometer

Post by CrabbyLover77 » Mon Mar 23, 2020 11:53 am

Motörcrab wrote:I would probably just keep it. If you are trying to keep 80% humidity you just need to remember to add 5 for 85%. If it drops below 80% you know your humidity is low.

For a while I was paranoid with humidity after a Zoo Med gauge stopped working. Our substrate got too dry and I dried out a molting crab. For a while we kept two gauges in our tank for double redundancy.

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Ok that sounds good. I've got about 3 hours to go for the final reading, then I'll put it in the tank and remember to add 5%. So much for the unit being "Pre Calibrated" like it said in the description lol. Image
I forgot my alarm clock has a temp and humidity gauge on it. I just started to calibrate it now. If that's more accurate, I'll just buy another one of those for my alarm clock and use the 2 digitals in my tank.
Thanks again for all of your help!

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My Pets: 1 Pomeranian, 1 Russian tortoise, fishes/snails(40 gal freshwater aquarium), and 4 hermit crabs.
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Re: Calibrating a hygrometer

Post by CrabbyLover77 » Tue Mar 24, 2020 11:24 am

After 24 hours, my new hygrometer was 5% too low.
I calibrated my alarm clock that has a humidity gauge yesterday too. It was only 1% too low.
I think I might just return the new hygrometer and use my clock with humidity and temp on it as my gauge instead. I should have checked that first and I wouldn't have had to buy one lol. I can just use Alexa/Echo and my phone for an alarm.

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Re: Calibrating a hygrometer

Post by KimzKrabs » Tue Mar 24, 2020 11:30 am

That’s a good idea! It seems to be that way isn’t it lol we buy we return we buy we return lol right now mine is 4% difference. The fogger timer says 82.9 the digital in the tat says 76 hmmm? I’m just gonna assume all is good in there most are molting anyway I just watch all day and try to keep it regulated within about 5 % or so 🥴

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Re: Calibrating a hygrometer

Post by CrabbyLover77 » Tue Mar 24, 2020 11:58 am


KimzKrabs wrote:That’s a good idea! It seems to be that way isn’t it lol we buy we return we buy we return lol right now mine is 4% difference. The fogger timer says 82.9 the digital in the tat says 76 hmmm? I’m just gonna assume all is good in there most are molting anyway I just watch all day and try to keep it regulated within about 5 % or so Image
Thanks! I totally forgot that my alarm had humidity and temp on it when I ordered the small hygrometer on Amazon. Duh, hahaImage My Dad calls my Mom and me the Queens of returns lol. But hey, if it doesn't work or is damaged, I'm not going to waste my money. Image
I agree, regulating within 5% sounds good, especially if everyone is doing well. Image

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Re: Calibrating a hygrometer

Post by CrabbyLover77 » Tue Mar 24, 2020 4:27 pm

I think putting the gauge in the container and then a ziplock wasn't air tight enough. I used 2 ziplock bags for my alarm clock and got 74% after 24 hours. So I decided to put the new gauge in 2 baggies and recalibrate. After 2 hours it's already fluctuating between 71-72%. It took hours to get to that point before. Maybe I won't have to return it after all lol.

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My Pets: 1 Pomeranian, 1 Russian tortoise, fishes/snails(40 gal freshwater aquarium), and 4 hermit crabs.
"Animals are my friends, and I don’t eat my friends".
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