Thermometer Frustration

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dward0487

Ever since I built my tank, I've had a JW magnetic thermometer in it, which tells me that the water is right at around 79.5 or 80 degrees F. I was pleased with this, and everything seemed fine in the tank. However, I recently acquired a Milwaukee pH meter, and while I was taking my pH reading, I noticed that the temperature probe on the meter was reading 27.5 degrees C (81.5 degrees F). I was concerned since this was about 2 degrees higher than what my magnetic thermometer has been showing me. I decided to go pick up a digital thermometer for constant monitoring that might be a bit more accurate than the magnetic one, so I bought the little Coralife black digital model, and installed it in the tank. To my surprise, the thing reads 82.4-82.6 degrees F! I'm getting really frustrated here, because it seems like no two thermometers ever read the same in my tank. These temps are mostly in the top range of what would be considered acceptable (although the inhabitants seem fine), and I'd like to adjust my heater to get the temp slowly down to around 80 or so, but I have no clue which thermometer to believe. Any thoughts or suggestions?
 
Buy an old school mercury style thermometer to get a baseline. Only way to know for sure IMO. Even the tank controllers 'lab grade' probes are never dead on. The apex even has a correction built in to the software for you.

This is the one I use - http://www.drsfostersmith.com/product/swatch_image.cfm?window=1&prod=3921&ranknum=3&thumbid=10471&thumbpage=1&list=10469,10470,10471&breeds=1
 
You'll find thermometers really vary unless you get one that is calibrated or traceable to NIST or something similar which are expensive. Perhaps one used in the medical field to take your temperature to see if you have a fever might be more accurate?

If you are concerned about running too high a temperature, what about shooting for something like 78 degrees to give you a little leeway on the upper end? My personal experience has been keeping a consistent temperature is more important than a variation of a degree or two between what my system runs at vs. someone else's system.
 
Wes, that looks like an alcohol thermometer rather than a mercury one. I'm not sure where I'd find a mercury thermometer these days, and if it somehow broke in the tank, my fish would be in trouble! I'm guessing you are just referring to the analog tube style of the thermometer. I actually have one of those in the tank already (the JW magnetic is a tube-style alcohol thermometer). It's the one that reads the lowest of all of them, but I doubt its accuracy. I'm used to using lab thermometers because I'm a scientist, and they usually have the degree scale actually written within the thermometer glass itself, while all the aquarium thermometers I've seen have the degrees written on a separate piece (e.g., on a card that is glued to the thermometer in the housing, or on a piece of plastic within which the thermometer sits). I worry about these types, as simple error in the positioning of these separate pieces when assembling the thermometer can cause it to give an inaccurate reading.

Mike, your idea about shooting for a lower temp is a good one, and it's actually what I'm trying to accomplish. I have an Eheim Jager heater, and I calibrated it with the red indicator to the current temperature of the water (which I estimated at around 81.5 degrees, given what I've seen with the thermometers). I turned it back on and set the blue dial to a water temperature setting of 79 degrees, and gave it time to settle in. The heater light turned off, and I figured I was good to go. This morning, my water temperature was around 81.3 (using my pH meter's thermometer), and I noticed that the heater light was back on... I have no idea why the heater is still coming on after it has been calibrated and set to a lower temperature. I went ahead and backed the blue dial off a degree or two more, and we'll see how it works out. It may be that I simply can't get the temperature any lower in this tank. I don't really have room for a chiller... From what I've read, 81 degrees is alright for a reef, and I'm aware that consistency is more important than the actual temperature. I never really see any fluctuation on the thermometer throughout the day. I suppose if all my inhabitants seem to be doing well, then 81 will be fine. What do you think?
 
If you want to get the tank cooler, and assuming your ambient air temperature is lower, you could always try using a small fan to assist with evaporative cooling. That said, if everything in your tank is doing well then I would just leave things as they are. If it ain't broke, don't fix it. [smilie=smile.gif]
 
@Mike wrote:
If it ain't broke said:
That's usually my motto, but then again, I am a bit of a perfectionist. If I can't get something EXACTLY how I want it, I tend to get a little frustrated and obsess over it. I'll see how the temperature sits over the weekend, and I'll post an update on this thread reporting my findings. The fish and corals seem happy, so that's a good sign. Thanks for the help!
Click to expand...
 
Yes, that's all I'm talking about which is why I said mercury style. The most important thing with temp is not really the actual temp, but having a stable temp. Something around 78 is best but if you are holding a stable 81 then you should be fine. There is a pretty wide range that is acceptable so we are just aiming to be close. Like mike said, if your tank has been like this for a while and everything is happy then why change? In the summer mine hovers around 79.5-80 and the winter it's around 78, or at least that's what my controller says.
 
Well, I came home today, and the temperature was right at 80 degrees when measuring with the pH meter (which seems to be my middle ground, in terms of temperature measurement - - I'm using it as my baseline). It looks like the heater adjustment worked. I'm adjusting to around 79, and then I'm going to hold it there.
 
I had the same problem. Almost bought one of those NIST thermo's but read the fine print and even those say they have a margin of error of 1.5 degrees. Ended up going to Petsmart and they had a few different mercury type thermometers and multples of each that were all very close. A few were off from the rest (like you said maybe the card was misglued) so did not pick one of those. Mercury has been working pretty good for a few centuries so I do trust those. I really would not worry about one busting in the tank.
 
Wow, Petsmart had mercury thermometers? Is the liquid in the tube silver, or red? I've only seen red these days, and those are alcohol. Still pretty reliable, though, just safer.

My water temp is around 79.5 right now. I'm just waiting to see when the heater light kicks on so I know where it will keep it. Hopefully it won't get too much colder.
 
Well, the heater kicked on right around 78.8 degrees (based on my pH meter thermometer), which is exactly where I want it. It should keep my temp at an even 79. My digital thermometer reads 80.1, and my glass thermometer reads 78. Any way you look at it, the temp is good. I think we're done here. :)
 
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