Coralife Digital Thermometers - My Observations

[BigDaddy]

I will start by saying this is simply an observation of ONE unit in one non-controlled environment.  However, even under those conditions, I found this a bit more than disturbing.

My heavily planted tank has a 4 x 54 HO lighting unit over it.  The DIY box is not actively cooled, but rather has a large slit across the top to allow for simple convection to deal with the heat.  Heat is an issue, the room the tank is in is always warmer than other rooms in the house.

At the far end of this tank sits a Coralife Digital Thermometer.  Those of you who own one now it comes with a fairly lengthy piece of cabling between the probe and the unit itself.  While the majority of the cable is submerged, some of it sticks out past my glass top and wraps around the top of the tank to the unit which is stuck to my trim.

So.. just to see if some active cooling of my lighting unit would actually make a difference in the room temperatures I took a normal household fan and placed it on the hood pointing down into the vent opening.

What I watched happen afterward had me raising eyebrows and asking questions.

Within the span of less than 5 minutes, my Coralife temperature reading went from 80.9 down to 80.1 and back up to 80.9.  The probe in the tank was never disturbed.  The cabling to the unit is not underneath the lighting unit, it sits on the trim well away from the DIY box.

There is no way 75 gallons of water drops almost a full degree Celsius in less than 5 minutes of its own free will, let alone come back up again in that same time frame.  The only thing that changed was the sudden increase in airflow OUTSIDE the aquarium while I was actively cooling my lights.

This leads me to think that somehow, the cabling is transmitting the ambient temperature around it as data, and not exclusively the probe in the tank itself.

I know DarkDep did some studies as well, and found that his digital thermometer was also somewhat inaccurate compared to a calibrated scientific meter.  Now, I'm not saying all digital thermometers are 'off'... but certainly two experiences from two different OVAS members under two completely separate setups both found the Coralife to be questionable in its readings.

I'd be curious to hear if anyone else has done any other testing of their own, or noticed discrepancies similar to this.

[fischkopp]

Do you mean the thermometer unit is attached to the tank or light fixture? If so the heat dissipation could heat up the unit itself it may cause a change of the operating point of its measuring amplifier. This will change the gain of the module, which finally leads to inaccurate measurements as the temperature probe signal is amplified a little bit different.

When you now cool down the environment you will also cool down the unit, change the amplifier gain and get a different interpretation of the probe signal (and hence different temperature shown on the display), although the probe signal itself hasn't changed.

Dont want to be to technical here (thats the engineer in me ), just a thought whats causing the inaccuracy of digital temperature sensors in this case.

[charlie]

I have several of them and really never noticed that with them, but i will say they are not accurate, i`ve put them all (5 ) in the same body of water & have 5 different readings, this holds true for the more expensive pinpoint as well. I also find the pinpoint to be useless, with a single  sensor it`s not bad but multiable sensors & it`s all over the place.

BD you can try it away from the lights & see what happens, place the probe in a jug ( bowl )of water & then try the fan.
Regards

[normc]

The one on my tank reads 29 C right now. I put in a large floating thermometer designed for wine making and it reads 31 and my stick on the glass shows > 30 the numbers only go to 30.

[speckledmind]

Interesting findings from BigD and Charlie 

I was thinking of adding one of these fancy doodas to my reef tank, but I guess I will stay with my $0.99 suction cup one instead 

[darkdep]

I think given recent observations, that there are only two ways to go to ensure accuracy;

1) Stick to the $0.99 glass thermometer.  It seems to be about as accurate as the "aquarium grade" thermometers get.

2) Spend the cash on a lab grade thermometer.  This is a pricey tool ($40-$100) but there's no wondering.  If you have sensitive fish, might not be a bad way to go.  I love mine.