Heating issues

[Davoaldo]

How do I know if a heater is getting old?

Which type of thermometer is better?
I have 2 in my tank and they vary in temperature by 2 degrees Celsius.

1 is the normal mercury type, where i read of a scale.
The other is a digital one http://www.thereefshop.com.au/index...id=138&zenid=771abd780e0e3e88a32803a9bb90317e
.


Now I am all lost and don't know which temperature to trust.

 

[JokerGirl]

I would trust the analog thermometer more than the digital. It's good that you're keeping two different thermometers in your tank. If your analog thermometer has mercury in it, I would change it out for one with the red liquid in it. You wouldn't want it to accidentally break and leak mercury into your tank as it is very toxic to anything alive including you.

The problem with digital thermometers, although very quick at giving you a reading, can be calibrated incorrectly or have something external giving a bad reading.