Thermometer variation?

[twelvejewelz]

I have a coralife digital thermometer and its currently readin 85F with the lights off and MY tank is usually 80F. Im wondering if these things go bad? I stuck one of those medal thermometers that hang on the side, the ones with the red mercury i believe, and its reading 80F. Do you think the digital one is craped out on me and that the medal one is 100% acurate? I put a new battery and its reading the same.Ive never had a problem with it before or atleast i dont think i have now im second guessing the thing.
thanks in advance!


EDIT: BTW the digital one is right next to a rio 90 powerhead. Do you think that the heat from the power head could be causing a faulty reading? Its always been there but is there a chance that the powerhead is possibly breaking and giving off more heat now in turn causing the temp next to the thermometer to rise?Should i just remove the PH?

[AaronM]

Yeah maybe move the PH and digi therm away from each other to test that, or you could move the merc therm as close to the PH as the digi and see if reads higher. If so, i guess close to the PH is warmer than the rest of the tank.

[bassking16]

I ran into this problem when I fist set up my Temp Controller. I went through about four or five different thermometers to get an accurate reading. Some mercury, and some digital, and all gave me a different temp.

I looked up on line about home calibration, and decided to try the "ice bath" method. Basically crush up some ice in a cup of water, and take the temperature. It should be right at 32 degrees F, give or take a little. I found the one thermometer that gave the closest reading to 32 degrees, and used that to take the temp of my tank. Then I just adjusted my temp controller to make up for the offset. Somewhat of a pain, but it worked. My temp controller reads 3 degrees higher then the actual water temp, but I accounted for that when setting the on/off on the controller.

Hope this helps.

[lordofthereef]

The above method works great that said if you have a favorite thermometer (perhaps one with a controller or something) you van always do the above steps and still use it if it's off. Simu adjust for how much it is actually off and you should be fine.

[Lynnmw1208]

I would say it was too close to the powerhead as well.

[crvz]

I like the logic of the ice bath "calibration", but unfortunately some of these thermometers drift worse over particular temperature ranges. For a thermometer that's designed with an expected operational range of say 70-90 F, I wouldnt trust a calibration test performed at 32 F.

To answer the OP original question, yes, digital thermometers certainly do go bad. I have been meaning to get a lab grade thermometer (think chemistry class) to better calibrate my systems, but have yet to do so. Time to go shopping, I guess.

[Korrine]

I had a coral life thermometer that always ran low on my cichlid tank(show'd 60's when it was higher than that). I chucked it and bought another, which appeared to be reliable.

[twelvejewelz]

Thanks everyone. I moved the digital around the tank and was getting all different readings. I took it out and put it in a bucket of cold sink water and it was reading 60degrees then i put it back in the tank and it went up to 87degrees. I think its just broken now. How reliable are the mercury thermometers? I need to get me a lab grade one as well who knows how long this thing was broken and i was seeing constant temp swings but nothing in the tank was affected! How safe is the steal in the water from the thermometer? I guess i go looking for a new one as well. Ive been meaning to get a Controller with PH, Temp and all that good stuff anyway so mabe the time is now. The new therm i have now is reading a steady 80degrees and i tested it with another plastic one and it read the same so i guess the coralife digi lasted 3 years not bad for about $5 lol .