# Digital Thermometer issue



## dewalltheway (Jan 19, 2005)

I have always bought and used the small Coralife digital thermometers but recently had an issue with one that I thought was reading not right. So, I did a test last night and stuck 5 of my digital thermometers in one tank and put the probes all in the sam area so I could see if they would all read the same. To my surprise and now my questioning, they all read something different from 68 degrees to 75 degrees. So......my question is, how do I know which is correct and are these thermometers able to be calibrated?


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## Cuchulainn (Nov 2, 2010)

Not sure if they can be calibrated or not....personally though, I would sell the digitals and go with an old skool $1.50 mercury thermometer. Between that and the thermometers built into the heaters, your tank should stay pretty consistant. Guess you could say, I think digitals are a waste of money


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## sdm (Jan 9, 2007)

I've been meaning to post a similar question. I've got about 6 of those cheap, $1.50 thermometers. I get different numbers from all of them when I put them in the same tank. I was going to try a digital but apparently they aren't much better. Can anyone recommend a reliable thermometer?


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## jiang604 (Dec 28, 2009)

sdm said:


> I've been meaning to post a similar question. I've got about 6 of those cheap, $1.50 thermometers. I get different numbers from all of them when I put them in the same tank. I was going to try a digital but apparently they aren't much better. Can anyone recommend a reliable thermometer?


msnikkistar has a few very reliable digi therms. My friend and I both have used coralife and have found theres a problem with them.


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## GitMoe (Aug 30, 2010)

My Zoo Med digital is 12 degrees off.... lol. I like to use nano glass thermometers from AZOO and now Fluval sells them out of the new Ebi line. I've seen them in local shops finally. Stick to the old school.


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## Sluggo (Nov 6, 2010)

IIRC, those Coralifes only claim accuracy to within a degree and a half, so you're going to see differences of up to 3 degrees if you place several of them in the same tank. 7 degrees seems like a lot, though.


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## JimT (Jul 14, 2010)

I just got the digital coralife, thinking it would be an upgrade from a ten year old radio shack digital. The radioshack has the room temp, humidity, and the remote. I didn’t trust it, and the cord is white. Anyhow, I’ve had them both in there for the transition. I checked them with a thermocouple and the 10 year old radioshack agreed within 1/10 of a degree and the brand new (this week) coralife agreed to about 1.7, some times more. I had them within the same inch of space. Not an official experiment. I bought the coralife because it was black and I like digital.


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## bsmith (Jan 8, 2007)

Coralife digi therms are the worst ever.


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## rickztahone (Jul 20, 2009)

bsmith said:


> Coralife digi therms are the worst ever.


+1. I use the cheapo glass ones and then I just know how much the digital ones are off by and I measure the temp accordingly. So if my digital reads 80, I know the temp is 84. The good thing about the digital ones I have used is that although they are inaccurate they will be off by that specific number pretty much all the time.


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## Tunze (Sep 3, 2008)

Most digital pocket thermometers have a potentiometer in them.
You might be able to pop open the case and adjust the potentiometer to calibrate your thermometer.


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## QC Discus (Oct 25, 2010)

*How do I calibrate a digital thermometer?*

*How do I calibrate a digital thermometer?*



Ice point.

Fill an insulated glass ( styrofoam cup works well ) with crushed ice and then add a little water. 
Let it sit for at least five minutes and then insert the sensing part of the
thermometer into the cup.

Make sure the sensor is in the middle of the glass and at least an inch from the sides, bottom, and top of the glass.

Hold it there for 90 seconds or until the dial stops moving or the digital thermometer beeps.

Your thermometer should be reading 32 degrees Fahrenheit after 30 seconds. If it’s not, it needs to be re-calibrated.

If there is no calibration nut then simple math is used to determine if the thermometer is reading high or low.

The ice point method is the most accurate way to calibrate a thermometer.


Check out my help page for Calibrating the boiling point method .
QC Discus help


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## Wasserpest (Jun 12, 2003)

Unfortunately, calibrating to boiling and freezing point still does not guarantee that it will be absolutely correct at 76F.

Also, some digital thermometers can suffer from electronic interference, they might be all over the place if placed near ballasts and other noisy things.

Best thing is to compare to a good analog thermometer. I use these thermometers which are easy to read and pretty spot-on. Not easy to find over here.


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## jjlin78 (Aug 15, 2009)

this is good to know, i have a coralife digital thermometer and have never thought that it could be off by so much. i've always wondered why it is that when i set the temperature on my hydor eths that the temps in the tank with the digital thermometer is always different. so how accurate is the temperature dial on hydor eths?


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## dewalltheway (Jan 19, 2005)

jjlin78 said:


> this is good to know, i have a coralife digital thermometer and have never thought that it could be off by so much. i've always wondered why it is that when i set the temperature on my hydor eths that the temps in the tank with the digital thermometer is always different. so how accurate is the temperature dial on hydor eths?


Thanks to everyone who has commented and made suggestions. jjlin, I will answer your questions in a minute. I took QC's advice a took a styrofoam cup put about 4 ice cubes in it and then a little bit of water, let it set for a few minutes and then tested each one to see how close they got to 32 degrees. I then marked each one with either a minus or plus so many degrees based on their reading and found one that was a few tenths of a degree off from 32 and called that thermometer good. I then took them all back to the aquarium and put them back in and saw where they read. I have a inline Hydro heater and it is set to around 75-76 degrees, so when the one that I called good read 75.5, I knew I was getting a good reading. As it turned out, all the other thermometers read to the plus or minus of 75.5 that I had marked on them...ie. I had one that read 1.4 degrees more then 32, so when I placed it in the tank it read 76.9.

Now...jjlin78, to answer your question, I would trust a inline Hydro heater. I have had that heater for several years and it has been very realiable and with this test shows it is spot on what it is set at.

What I have found is that these Coralife thermometers can and will read off so check them. In my testing, I had one that read almost -10 degrees off, one -7.4, one +1.4 & one +2 degrees. As a side note, I put new batteries in all these thermometers before doing my test so I knew the batteries where good.

Thanks again to all!


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