Where to get accurate thermometer????


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Hey all, just wondering where I can get an accurate thermometer from around here?

Tony was kind enough to give me one, but I don't think it is terribly accurate.

I hear of people getting a scientific or whatever it's called, thermometer that has a range of 75 or so to 88 or so that's made of glass, that's supposed to be really accurate, but I don't have the first clue as to where I would go to find one.

I don't want to spend alot of money on this, but I want something that is accurate. A couple degrees difference would mean the difference between needing a chiller and being able to get buy with a couple cooling fans.

What are you guys/gals opinions? Advice?


Well, that's my problem. I don't know where I am sitting at.

I just checked my tank and it says 81.5 degrees. It's cool in my living room, where the tank is, it is 12:45am, 63 degrees outside, no top on the tank and the back and r.side of my stand are open for ventilation. The only thing in the tank is a Tunze 6000 and a heater that is unplugged, along with my skimmer. 2 external Blueline 55's are my pumps.

So, if the therm is accurate, then I can expect to be close to 88-90 once I build a canopy and install 2 x 250w MH + VHO/PC lighting.

This situation would definitely warrant a chiller.

On the other hand, if the therm is a couple degrees off on the high side and I am actually around 78-79 degrees, then I believe a couple cooling fans in the canopy will be able to cool off the heat being generated by the lighting and maybe only have a +2 degree swing once the lights come on.

Big difference between spending $300-$500 on a chiller and utilizing 2 fans that I got for free, that are sitting in my garage.

I understand that accuracy isn't as important as stability, in terms of aquarium keeping, as long as you are in the acceptable range, but you have to have an accurate starting point first.
Cheap Coralife Digital thermometer.

I talked to Tony at the last meeting and he said something about being 4 degrees off when he had it. At least, I think that's what he said. Plus, Coralife says that the thermometer has a 1.5 degree tolerance, which is pretty big in itself, let alone add in a difference in calibration, could easily get to 3-4 degrees off.
How do you calibrate it?

And it does work just fine, but I want to know how accurate it is, compared to a thermometer that is known to be accurate, which is why I started this thread, to find an accurate thermometer to compare it to what I have now.

Anybody know where I can get said thermometer at?
Have a look at these digital thermometers from Fisher Scientific, +/- 1 degree.

RazMatic wrote: Have a look at these digital thermometers from Fisher Scientific, +/- 1 degree.


Thanks Raz,

I ended up going with one from Drs Foster and Smith.

Here is the link:


It is accurate to .5 degrees and also has a re-cal switch on the back which sends a signal of 32 degrees +/- .5 degrees to re-calibrate it.

Also, it is on sale too.

The actual temperature isn't as important as stability. And the type that Tony posted a picture of (the mercury type) is probably about the most accurate you'll find, although not very precise.

My recommendation? Buy a ReefKeeper2 to monitor your temp and control everything else at the same time. I can't guarantee that it's good to 1 billionth of a degree, but it is very stable and directly usable in your system. (Don't you already have a RK2??)
I wish I had one.

I understand the concept of needing stability over trying to keep a certain temperature, but my point to this whole thing is, if you don't know how accurate your thermometer is, then you have no clue what the temp in your tank is.

Example: I have read many threads of the Coralife digi therms being way off and I have also read of people saying they were dead on. I will refer to mine in a second. So, take my tank, where last night it says the tank temp is 81.something. I don't know how accurate that thermometer is, so if it is off by 3-4 degrees on the high side and my actual temp is 84-85 w/o a canopy, MH's, actinics, then I need to do something before I add the lights, ie chiller, multiple fans, etc.

Now granted, I did do the whole ice cubes in water in a cup and put the Coralife in there and it read almost 2 degrees low, but this doesn't guarantee that at higher temps, it will be the same difference off.

So, I bought said thermometer above and got it last night. Here is what I found:

- First off, the thermometer read exactly 32.5 in the cup with ice cubes and water, being swirled around. Talk about being exactly .5 degrees off. I was extremely happy.

- Next, I stuck it in the water and found that it read 82.3, which really surprised me. Even more shocking was the fact that the Coralife was reading 81.6. So the Coralife is almost within it's own tolerance of +/- 1.5 degrees.

But the moral to this story is: You need something accurate to give you a good baseline to set all of your other thermometers to. I NOW know that my Coralife is 1.7 degrees low. I don't have to guess or assume anything. I know this for fact.

Now, I can make the adjustments I need regarding fans and chillers b/c I know the accuracy of my thermometer. And I can now spend more time trying to keep my tank stable, b/c I know what to add to my thermometer to make it accurate to what temps I want to keep the tank at.

I, personally, would highly recommend this thermometer from Drs Foster and Smith. It's cheap, accurate and a good thermometer to have around to determine the accuracy of other thermometers you may have and also to calibrate temp probes for controllers, such as the ReefKeeper II, which allows you to adjust the temp for calibration. And to top it all off, it is even on sale for less than $28.
I went through the same thought process of trying to calibrate thermometers, and realized that, unless you use some specific chemical reaction, it'd difficult to find something that will give a precise temperature that you can calibrate off of. Even icewater is questionable for calibration- can you say that the calibration scale isn't affected at temperature extremes? It may be off by 5% at freezing temps and only 1% at 80 degrees, or vice versa.

I finally just started collecting several thermometers over the years and use them all from time to time- as long as they don't deviate from each other very much, I'm not too worried. Corals will be ok even up at around 86 (although you'd have no room for error), so even an error of 5% means that my 81F reading is ok, as long as it's consistently that far off...