Pentair Big Digital Temperature Alert-gone bad

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Aquarium Advice Addict
Feb 17, 2003
Belle Mead, NJ
When I replaced one of my heaters a few months back the temp readout on that was off a few degrees from the Big Digital so I checked both against mercury thermometers including a lab grade mercury thermometer. Both mercury thermometers and the Big Digital gave the same temperature.

The other day I noticed that my tank temp appeared to have dropped by 5 degrees. My Big Digital Temperature Alert was reading 75 when it normally reads at 79-80.

I nudged the controller on both heaters to make them turn on and felt both of the titanium heaters to make sure they were getting hot. They were.
I then put my cheap mercury thermometer in the tank and it was reading a normal 80 degrees. Hmmm... One of them is wrong, so I double checked with my lab grade thermometer and it too is reading 81 degrees (the tank heated up 1 degree due my nudging the heaters up a notch).

I took the Big Digital Temperature Alert out, cleaned the temperature probe of coraline algae, and then tested it against both mercury thermometers. It consistently read 5 degrees lower.

After 10 months of reliable service this digital unit is now a consistent 5 degrees off. As long as I'm aware of that I'm ok with it. If I had not checked it against a mercury thermometer my tank would now be at 85 degrees :eek: :mad: :(

I sent an email to Pentair Aquatics and I'm now waiting for a response.
Keep us posted... I've got one of those also, but it's one of three total thermometers (not including the controller readout!) so I'm thinking I'll catch mine if it goes bad. I had a Coralife in my SW mixing tub do that on me one time... just suddenly read out a totally wrong temp.

Is your Big Digital in a place where it could get salt spray in it?
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