temp. probe test

[mpgrant77]

So I have been running a reef keeper since I started my aquarium at the beginning of this year. It always bothered me a little because I got this feeling the water was a little warmer than it said. I put a little digital temperature monitor in to test it and they were off two degrees. I figured that the new reef keeper would be more accurate than a cheap 10 dollar digital thermometer. Recently I bought a used Apex that I am going to upgrade too. I have both systems on the aquarium and the temperature probes were reading 3 degrees difference. This had me a little concerned so I did a test. I brought home a digital temperature meter from work. Lab grade. I used my cheap digital thermometer and a nice kitchen monitor with temperature probe. I placed all 5 probes in the same area of the tank and let them sit.
reef keeper - 79.9
Apex - 83.0
Kitchen probe - 82 (only whole degrees)
cheap digital temp - 81.7
lab meter -81.9
<a href="http://s292.photobucket.com/user/mpgrant77/media/Aquarium/2000D887-F3D8-47D8-8339-27C0E2EFB990.jpg.html" target="_blank"><img src="http://i292.photobucket.com/albums/mm37/mpgrant77/Aquarium/2000D887-F3D8-47D8-8339-27C0E2EFB990.jpg" border="0" alt=" photo 2000D887-F3D8-47D8-8339-27C0E2EFB990.jpg"/></a>

The two less expensive items seemed to be reading pretty close to the lab meter. But to my surprise neither the apex or reef keeper was correct. It is good you can calibrate them. Now everything says the same thing. It just surprised me that they were both off. I would think that most people do not have easy access to a meter to calibrate temperature probes so they should be good from the get go. I know that it is more important to keep the temperature steady and that being off a degree or two is not that big of deal as long as it is constant. But for the money spent I expected a little more. I thought I was at 80 with two degrees to play with both sides but I was actually 82. Which means my tank has been up to 84-85. I have been having issues with my SPS lately and maybe this is one of the reasons.

 

[Schplitter]

Found out the same thing you did with both systems being way off. I bought 7 different thermometers and took the average of those as a good point for the apex to be set to.

 

[Breto]

For those who don't have a lab grade temp probe one of the best and most accurate ways to calibrate is with an ice water bath. The process is quite simple and for what it is it's really pretty good.

 

[mpgrant77]

I tried the ice water bath with the lab meter and the apex and could not get the temp down to 32 the best I could do was about 38 so be careful with the ice bath.

 

[Mr D smack]

I tried the ice water bath with the lab meter and the apex and could not get the temp down to 32 the best I could do was about 38 so be careful with the ice bath.

Did you use crushed ice?

 

[mpgrant77]

I did not. Glass full of ice and some water. The crushed ice would probably have been better.

 

[u4ick]

For those who don't have a lab grade temp probe one of the best and most accurate ways to calibrate is with an ice water bath. The process is quite simple and for what it is it's really pretty good.

As explained to me by Neptune.
Apex uses a highly accurate thermistor in their probe, and so as such it's accuracy is good in a a specific range.....being 65*-95*. Outside those temps and it becomes less accurate, however the drift is not linear....meaning if it's off by 1 degree at 60, it would be off by more than that at 50*, and even more so by 40*....not just a basic 1* all the way up or down.....(interestingly enough this is also true of refractometers).
So calibration should be done with-in the working range of the item to ensure it's accuracy.....so the ice water method for an Apex probe would not be the recommended method.