Aquarium thermometers - Why do I get different readings?

[Tradewinds]

I'm trying to dial-in the settings for my tank, one of which is getting the temp stable. I bought two different brands of aquarium thermometers, one for the QT and one for the DT.

When placed in the same tank, in the same location, I get two different readings. One displays 77 degrees, while the other reads 81 degrees. I have shaken both of them down, but when placed back in the tank I get the same readings.

I have the heaters set at 78. How do I know which thermometer is correct?

[thegrun]

I purchased a quality lab grade glass thermometer years ago and use it to calibrate all my other thermometers. Never trust the markings on a heater; I've seen them off by more than 4 degrees.

[jeff@zina.com]

How do I know which thermometer is correct?
Average a few dozen. :)

Thermometers are never accurate. Once you accept that fact, you'll also accept that heaters are never accurate either. One of the reasons controllers exist for reef tanks. Or use a Ranco controller.

Besides, the live stock doesn't care about exact temperature as much as a relatively steady temperature.

Jeff

[firebirdude]

Average a few dozen. :)

Thermometers are never accurate. Once you accept that fact, you'll also accept that heaters are never accurate either. One of the reasons controllers exist for reef tanks. Or use a Ranco controller.

Besides, the live stock doesn't care about exact temperature as much as a relatively steady temperature.

JeffBullseye.:bum:

[cloak]

Those stickers you attach to the side of an aquarium have never steered me wrong.

FWIW.