# A good reliable Digital thermometer



## Mr Dinks (Sep 23, 2008)

I don't trust just one thermometer so i have opted to go digital as well as michanical if you see what i mean.

Can anyone from experience reccommend one?


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## prov356 (Sep 20, 2006)

I bought a few because they're be easier to read. They were in the $20-$30 range. Pretty much 
junk. You might be better of just getting two of the typical glass variety since they're so cheap.


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## ercnan (Aug 13, 2006)

I use the standard glass w/suction cup in tank, as well as this
http://www.petmountain.com/show_pro...shoppingdotcom&utm_medium=cpc&utm_term=509748
Both read the same if placed at the same level in the tank, so I go by the digital mostly.
The glass is just sort of a control/back-up.


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## boredatwork (Sep 14, 2007)

So I am curious why people think digital thermometers are bad? Personally that is all I use so I really have no basis of comparison, but here is why I am confused. A digital thermometer is not really digital - in fact there is no such thing as a digital thermometer. Only the display part is digital. It should be called an electric thermometer or something. I don't know what specific part is commonly used for the sensor, but for the typical temperature sensor used in electronics the resistance of some material changes linearly with temperature. That resistance is measured and translated into a degree number But it should be at least as accurate as an alcohol thermometer. If even just for the fact that the alcohol thermometer its harder to read. I have built electrical temperature sensing devices and I have never come across one that is not at least accurate to 1 degree.

I am working on two theories. One is that since they are more accurate they show variation easily so they might seem inaccurate? The other is that people tend to have an unfounded distrust for anything electronic. There certainly exists the phenomena of believing that the good old way is the better way.

Or maybe, which is usually the case, I'm missing something.


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## prov356 (Sep 20, 2006)

Seeing the one that *ercnan* listed jarred my memory a bit. I have that one actually on my main 
tank. As far as I can tell it works fine. The ones that I'm not happy with I bought several of and they were
actually in the $6 range. I didn't want to spend $30-$40 each to cover several tanks. So, I guess you get 
what you pay for. I know they're bad because they're always off by a few degrees. This isn't hard to 
determine. I ran downstairs to double check them because I just added glass thermometers. The 
digitals read 74-75 degrees or so and the water is NOT that cold. You can tell water temp after you've 
been doing this long enough. The water feels right and the glass thermometers confirm that.


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## ercnan (Aug 13, 2006)

boredatwork said:


> So I am curious why people think digital thermometers are bad? Personally that is all I use so I really have no basis of comparison, but here is why I am confused. A digital thermometer is not really digital - in fact there is no such thing as a digital thermometer. Only the display part is digital. It should be called an electric thermometer or something. I don't know what specific part is commonly used for the sensor, but for the typical temperature sensor used in electronics the resistance of some material changes linearly with temperature. That resistance is measured and translated into a degree number But it should be at least as accurate as an alcohol thermometer. If even just for the fact that the alcohol thermometer its harder to read. I have built electrical temperature sensing devices and I have never come across one that is not at least accurate to 1 degree.
> 
> I am working on two theories. One is that since they are more accurate they show variation easily so they might seem inaccurate? The other is that people tend to have an unfounded distrust for anything electronic. There certainly exists the phenomena of believing that the good old way is the better way.
> 
> Or maybe, which is usually the case, I'm missing something.


You are correct.
It is a variable resistor, or more correctly, a thermistor.
It changes resistance based on temp.
The display is calibrated by a typical thermometer, but appears more precise, because it "shows" (typically) tenths of degrees via a displayed number you can see.
"Standard" glass thermometers do as well, you just can't see that small of a change in a tube of glass with a volume of mercury, and only a 2-3 degree graduation in change (typical glass merc. thermometer sold for aquariums).


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## Guest (Oct 28, 2008)

I use Coralife's Digital Thermometers. Mine appear to be pretty accurate when I compare them to my glass thermometers...

Here's one: http://www.drsfostersmith.com/product/p ... atid=12089


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## ercnan (Aug 13, 2006)

prov356 said:


> Seeing the one that *ercnan* listed jarred my memory a bit. I have that one actually on my main
> tank. As far as I can tell it works fine. The ones that I'm not happy with I bought several of and they were
> actually in the $6 range. I didn't want to spend $30-$40 each to cover several tanks. So, I guess you get
> what you pay for. I know they're bad because they're always off by a few degrees. This isn't hard to
> ...


Price does not always equal quality for one.
"Feels right" is not a valid statement either, no matter how long you have been "doing this".
If your glass thermo. is not right next to your digi. sensor, you have an error factor right there.
i.e. depth, circulation patterns in the tank, proximity to heaters, etc.
I'm not saying digis. are junk, or mercs. are junk.
I'm only saying that my merc. backup, right next to my digi. probe is the same as far as the definition of the merc. allows (it has a scale of 3-5 degrees, versus the digi's tenth of a degree).


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## prov356 (Sep 20, 2006)

> "Feels right" is not a valid statement either, no matter how long you have been "doing this".


What's not valid about that statement? :-? I can tell very easily by feel if my water is within the correct range for my fish. It's very easy to do.



> Price does not always equal quality for one.


I also know price doesn't always equal quality. Most learn that by a very young age.

So, not sure, but sounds like you're trying to lecture me a bit? You're probably not old enough to do that.


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## ercnan (Aug 13, 2006)

> So, not sure, but sounds like you're trying to lecture me a bit? You're probably not old enough to do that. Smile


Though I'm half way to 92,  no lecture was was meant  
My apologies if it came across that way  .


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## 24Tropheus (Jun 21, 2006)

My guess is the digital types have more to go wrong and can be affected by magnets.
But I do not use them so I have no direct evidence.
Mercury ones have been banned here I think for safety reasons (Mercury toxicity to humans I think)

I like simple alcohol ones but if they are cheap check them against a reliable make.
I had two same cheap aquarium make that showed a 3 F difference.
They were fine if you took an average. :lol:

I do know we went back to the old type at work (used as a independent measure of water bath temperatures) because we found the digital ones did not last with hard ware (wires became worn and gave up too quickly) and seemed less accurate over time.

There may be some reliable (cheap) ones but we found non.

Although the electronic ones claimed a finer reading the measure was not found to be as accurate given normal working conditions.


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## boredatwork (Sep 14, 2007)

ercnan said:


> You are correct.


I know.



ercnan said:


> It is a variable resistor, or more correctly, a thermistor.


A variable resistor is called a potentiometer.



ercnan said:


> It changes resistance based on temp.


The resistance of any material, resistors included, varies as a function of temperature. The equation for the resistance of any material always has a temperature coefficient. And a thermistor is a particular temperature sensitive resistor.

:wink:

Those were all useless comments that I just made. I couldn't help myself.

What I really wanted to address was that I didn't really see any evidence or convincing argument about the inaccuracy of an "electronic thermometer with a digital display".

Also, I didn't really understand the points about the decimal point accuracy of an "electronic thermometer with a digital display". The alcohol thermometer technically provides far more continuity of temperature readings as it has an infinite number of temperatures between any 2 consecutive degrees whereas the "electronic thermometer with a digital display" only has 10. So technically you are losing accuracy with an "electronic thermometer with a digital display". But I don't think anyone cares if the thermometer reads 72.9 instead of 72.8625.

Although if you can read the alcohol thermometer to the 10th of a degree you can probably deduce water temperature without a thermometer. Sorry, I couldn't help myself.

Lastly, an "electronic thermometer with a digital display" is not affected by magnets. That is a strange statement.


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## ercnan (Aug 13, 2006)

> A variable resistor is called a potentiometer


What then of a thermocouple ?
Wait, that's a device based solely on temp. rise/fall via expanding/contracting gases, no resistance needed (electronically speaking).

Potentiometers by "common" design are mechanical, adjustable devices used to turn up/down volume, and/or change the channel.
In this application (aquariums) they provide the end user a means to "turn up, or turn down" the heat.

Temp sensors, regardless of the design (potentiometer, resistor, diode, thermocouple, etc.) are not adjustable. They are built to a specific calibration (accurate or otherwise) and set.

Apples to Oranges here I feel.
Though correct technically, a little too technical for this intended application.
Speed controls for model trains, slot car tracks, variable speed tools, lighting dimmers, etc. I'll agree.


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## ercnan (Aug 13, 2006)

> Lastly, an "electronic thermometer with a digital display" is not affected by magnets. That is a strange statement.


I agree. I just put my mag-float next to the sensor, and have seen no change in display.
A big sub-woofer magnet will however, change my monitor display.


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## prov356 (Sep 20, 2006)

> What I really wanted to address was that I didn't really see any evidence or convincing argument about the inaccuracy of an "electronic thermometer with a digital display".


I have no idea about the science behind these things. All I know is the cheaper ones that I have don't work well.

This one works fine for me, this one does not.

HTH Mr Dinks.


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## boredatwork (Sep 14, 2007)

prov356 said:


> I have no idea about the science behind these things.


No one really does, we all just pretend.



prov356 said:


> All I know is the cheaper ones that I have don't work well.
> 
> This one works fine for me, this one does not.


If they show different temperatures in the same application then I would consider that convincing. Perhaps I will try to convince myself with some experiments.


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## ercnan (Aug 13, 2006)

prov356 said:


> This one works fine for me.


For me as well.


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## Marconis (Feb 9, 2007)

http://www.drsfostersmith.com/product/p ... atid=12089

I have that one and it is exactly the same as my glass one.


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## boredatwork (Sep 14, 2007)

Marconis said:


> http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=12089
> 
> I have that one and it is exactly the same as my glass one.


Hahaha. This is why we love forums - nothing like conflicting information.

That is actually the kind I use as well. In fact I have like 6 six of them, I use them everywhere. I also have an alcohol thermometer somewhere - never actually got around to comparing the two. I guess that could be step one.


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## boredatwork (Sep 14, 2007)

Also, how do people use their "electronic thermometers with digital display"? After thinking about it I thought about that question.

I use the coralife one and I notice that it uses some kind of averaging function so it takes a while for it to decide on the final temperature. Especially if I go from two drastic temperatures or turn it on and then stick it in water. Just like an alcohol thermometer its not an instantaneous number.

Not sure how the the others work but I was just curious how people use them in light of they seem to work.


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## justshoe (Mar 13, 2008)

I also have 4 of the coralife cheapies. They seemed to do just fine all are within 1 degree of each other and various glass thermometers that i have sittin around


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## Steve St.Laurent (Oct 2, 2008)

I went with this one - http://cgi.ebay.com/MARINA-AQUA-MINDER- ... 911.c0.m14 . It has a high and low temp alarm (you set the temps it goes off at) and also has three different maintenance reminders that you can set. Reads accurate to the glass thermometer I have as well.


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## prov356 (Sep 20, 2006)

Steve St.Laurent said:


> I went with this one - http://cgi.ebay.com/MARINA-AQUA-MINDER- ... 911.c0.m14 . It has a high and low temp alarm (you set the temps it goes off at) and also has three different maintenance reminders that you can set. Reads accurate to the glass thermometer I have as well.


That's a good price too for something with those features. I may try that one, thanks.


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## Sundog (Sep 16, 2006)

My experience is that the larger, more expensive one works well. I have 2 of the more expensive ones and they have worked for years. (3-4). I bought two of the cheap small ones as secondary backup thermometers and both were dead within 9 months. One with no display, and one reading 45 degrees in 80 degree water. The regular glass thermometer seems to work fine, the scale is just too small and too hard to read.


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## fishyfishyfishy (Dec 24, 2005)

Every one of my tanks has one of those adhesive ones that attach to the outside of the tank as a visual backup. They're easily seen when I walk by the tank. Super accurate no, but enough to provide a simple visual of something wrong.

All my tanks have digital thermometers inside the stand in one form or another. I did have one that woulnd't give a steady reading any longer. I called the manufacturer who advised to install one of those grounding probes as the probes can be sensitive to stray voltage. I hadn't made the connection that the problem started after I had uninstalled mine. Put it back in and sure enough end of problem.


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## boredatwork (Sep 14, 2007)

I finally got around to some experiments with the cheap Coralife thermometers. In my opinion, contrary to what I previously thought, they are no good. I tested three of them and one glass thermometer. All three of them gave different readings in the same water, and only one of them was close to the glass thermometer reading. Just FYI.


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## blairo1 (May 7, 2006)

I wonder what the thermometer is for....

For sitting in the tank and telling you the temp - go with glass. It's accurate and all you need.

If it's specifically for WC temp setting then I recommend digital - you're not going to wait for a glass one to show temp each time you fill a bucket, at least I don't.

I use something similar to the, CDN Pro AccurateÂ® Quick Tipâ„¢ Q2-450 Pocket Thermometer, although mine is for professional darkroom use so it's a little more expensive and probably more accurate. But if you read the tank temp with the digi quickly before setting the WC water at the same temp, it _will _match the tank temp. I say that with some confidence - although the reading may be out on some of these cheap digi's, it should at least be consistently out. Ie if it reads the tank temp as 27C and your WC water at 27C, you can bet they're the same temp (even though the _actual_ temp might be different.)


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## areuben (Jul 17, 2003)

I agree with this comment from Blairo1


> I say that with some confidence - although the reading may be out on some of these cheap digi's, it should at least be consistently out


I posted on another thread an experience I recently had with digis. I had the same concerns as voiced above with inaccuracies so I went out and bought 4 different brands and put them all in one tank, at the same spot with a fifth digi making for two of the same brand. Pentair read 82.2, Tom's read 81.4, Coral Life read 79.2 and 80.2 and Marina read 79.8. Two glass thermometers read approximately 79 -79.5, as much as you can tell from a glass thermometer and a small reading scale - but the glass were both the same. The bottom line for me was while the actual temps on the digis were all different (even with two of the same brand) and seemingly inaccurate, the fact was that they stayed constant and didn't fluctuaate over time. So, for example, if my Pentair stayed pretty much at 82.2 (really 79.5), I knew there weren't any issues. Still a pain that the actual reading is off, but it is still much easier reading a digi at a glance than reading a glass themometer up close. So, to get the right water temperature set initially, for me, glass is the way to go and most accurate.


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## Steve St.Laurent (Oct 2, 2008)

I have several of the cheap coralife thermometers that I use for my quarantine, hospital, and for getting the water temp right when doing water changes. What I did was put all 3 in my main tank right by a glass thermometer and the large digital I have in it. Then I made labels for all of them and wrote what the correction was. One read .3 degrees low, one .4 degrees high, and one read .8 degrees low. I have that written right on the front of them so I know what the actual temp is. I used my main tank as the set point since that's where they'll all end up in the end and as long as the temp is the same as that tank I'm set.


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## boredatwork (Sep 14, 2007)

My problem was I had three of them in use in three different tanks and assumed that they were all the same. And then I was using a separate one for WC. Now I just use one digital for WC, and glass in the tanks.


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## blairo1 (May 7, 2006)

boredatwork said:


> My problem was I had three of them in use in three different tanks and assumed that they were all the same. And then I was using a separate one for WC. Now I just use one digital for WC, and glass in the tanks.


 :thumb: That's the way to utilize them best IMO.


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## prov356 (Sep 20, 2006)

I'm feeling pretty low tech right now.  I just go by feel to get my change water temp right. What are you 
guys keeping and how much water are you changing that you're going for such precision?


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## travis2k (Apr 23, 2008)

the feels right method can work, but after a lot of water changes, youget used to the warm water and it can get warmer and warmer, I have taken buckets I thought felt right and found them to be at 90 degrees, which isnt a big deal in a big tank, but if you change 1/2 of the water in a 10 gallon that would take it from 80 to 85 degress pretty quick

Im changing one 55 two 30's and a 10 gallon right now and always use a thermometer, but I only try to be within a couple degrees.

the larger the % of water you are changing the more important the temperature is, and I beleive fish deal with an sudden increase in temp better than hey do a sudden decrease.


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## boredatwork (Sep 14, 2007)

I'm an idiot so I would never trust myself to do it by touch.

I usually change 25% on my 125. The problem was I was using one thermometer in the tank and one thermometer to adjust the tap water. When I compared the two in the same water they were off by about 6 degrees from each other. One of them was true to a glass thermometer, so that means the other was off by an actual 6 degrees. In all honesty I don't think it was really a problem, and I never noticed the fish doing anything that would indicate that it was.

The worse part is that I had another digital in a different tank, and that one was about 8 degrees off, in the other direction. This particular thermometer read on the high side, so it drove me nuts in the summer when the water would read at 90 degrees. Now I know that it was more like low 80's. But that tank is all guppies anyway and they are very accommodating.


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## TrashmanNYC (Dec 10, 2007)

my coral life digi reads 5* too low........


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## blairo1 (May 7, 2006)

50% water changes in all tanks - Tangs, SA's, Westies etc.

I do it with a digi because I like to be accurate, it's just how I like to do things, no other reason. I can get the gist with touch but it does tend to vary depending on how cold *I* am.


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