Unexpected Temp Problems

[andy]

When I got home last night, I was really surprised to find out that my tank temp had risen disturbingly high while I was at work. I have a Hagen Marina Aqua-Minder digital thermometer hooked up, and it was set to signal an alarm if the tank temp rose to 85.7° F or higher (yes, far too high – during our recent heatwave I raised it way up so it wouldn’t beep all the time. I was babysitting the tank and wasn’t worried about the temp since I was watching it closely. I just never set it back to 84° F). The alarm went off at about 3pm that afternoon, and my daughter (bless her heart) opened up the hood and connected the two clip-on fans I use to blow over the surface of the water to cool things down.

 

The tank temp was still hovering above 85° F when I got home at 6pm. The ambient room temp was 73° F, which didn’t strike me as odd at the time but would seem odd a bit later. I cut the metal halides and opened up the hood more, fully expecting the tank to drop back to it’s usual 78° F temp overnight.

 

So I got up this morning, and what did I find? 85° F. Room temp was still 73° F. What the hell was going on? I got worried… something was putting a lot of heat into the tank. The heater (Finnex Titanium with remote control) didn’t show as being on, and the pumps were all working normally. Thinking my heater thermostat had stuck somehow, and that the breakdown included one half of the bi-color LED (yeah, right…) I installed my backup heater. I know some people dislike the Finnex heaters, and it felt like I was starting to understand why. Then, something rather unexpected happened – the heater’s ‘active’ light ticked on. I double-checked the setting, and it was right on 78° F. Hmmm…

 

One of two things was going on. Either my backup heater had also failed (in a completely different way than the primary!) or… the tank really *wasn’t* at 85° F. Since I don’t have a backup thermometer, I had to come up with some other way of checking the accuracy of the Hagen. I *did* have a digital room thermometer, and I did have a bottle of water at room temperature. Good enough. First, I pulled the Hagen thermometer out of the tank, and used it to check the ambient room temperature. It read 75.7° F. The room thermometer read 72.9° F – a 2.8° F difference; not great, but not a *huge* difference.

 

Next, I checked the Hagen vs a liquid sample. Since the bottle of water had been sitting in the room for days, I knew it’s temp would be the same as the ambient room temp, 72.9° F. I put the Hagen’s probe into the bottle of water, and what did I read? 79.3° F, or a whopping 6.4° F difference!

 

So at that point, things were certainly pointing towards the Hagen as being the problem. My primary and backup heaters, plus the room thermometer all agreed. Still, I wasn’t sure how much I really trusted the Finnex heater thermostats and the room thermometer *could* have been off. Fortunately, I have a digital candy-making thermometer I use when making fudge; it is really accurate and precise, and I trust it completely. My fudge turns out awful, but that’s my fault not the thermometer’s

 

I dipped the candy thermometer into the bottled water. 72.9° F. I used it to test the tank. 76.8° F! Crap, my temp was LOW!

 

When I bought the Hagen, I believed that digital thermometers were all reasonably accurate and precise. The electronics inside are pretty-much standard off-the-shelf items and I figured if/when it had problems it’d look more like a complete failure than as inaccuracy. Clearly, I was wrong. I still think the electronics are likely reliable, the fact that the error is greater when the probe is submersed (2.8° F in the air vs 6.4° F in water) makes me think the problem is with the probe itself or the connecting wire.

 

Nothing bad happened to the thermometer to cause it to fail. It wasn’t hit, dropped, dunked, dripped-on or otherwise mishandled. It just broke. Fortunately, it broke such that it was reading high. If it was reading *low* during the recent heatwave, my tank could easily have been reduced to a 60 gallon bowl of chowder.

 

In the end, I guess this really isn’t that big a deal. I’ll contact Hagen and see what they say – I didn’t keep a receipt, so I’m not expecting much from them but we’ll see. However, it was a really good reminder of how important it is for us to keep our eyes open, to think critically and to have backups of all important equipment… even thermometers.

 

 

Pictures follow

 

Here's the Hagen showing the incorrect ambient air temp:

 

Here's the Hagen showing the incorrect ambient water temp:

 

The candy thermometer showing the actual ambient water temp:

 

The candy thermometer showing the actual tank water temp, fortunately well below the Soft Crack stage (laugh) :

[nu2reef-n]

Mr. Holmes, What kind of fudge is that? Why, salty my dear Watson.

Great detective work. I always run two thermometers. They sell those cheap little stick on ones for a dollar or two at most LFS.

[impur]

I always keep a few glass thermometers close so i can run a quick check on my electronic probe. Good detective work!

[andy]

Heh, yeah.. investigative overkill, I know ;-) Could'a just dashed out to the local GeneroPet and bought a glass thermometer, but sometimes the problem is more fun than the solution (laugh) (laugh)