i forgot to plug in a heater on a tank the other day and found the water pretty cold so i check the thermometer(aqua one in-tank thermometer) and it still read 28deg, so i put in a different thermometer and it read 24deg.

this got me thinking and thought i would do some test

thermometer used were

1. old school glass one

2. aqua one in-tank

3. aleas? some random thing i got from trademe, in-tank

4. aqua one external with internal probe

test one; good trust worthy heater set to 29deg

results

1. just under 29deg so 28.9deg

2. 29.2deg

3. 29.7deg

4. 27.7deg

test two; outdoor tank, no heater

1. 21.0deg

2. 24.6deg

3. 23.7deg

4. 19.0deg

last test; room temp

1. 21.5deg

2. 23.4deg

3. 23.8deg

4. 20.7deg

so which one is correct? no way it could of been 23-24deg in the outdoor tank

i use the good ol glass ones, they havnt failed me yet.

yep, go with the glass one

Unfortunately more thermometers are out in some manner. I really want a decent *accurate* one but they seem to be very difficult to find.

I have one which is supposed to be a scientific one for use in labs, but my other thermometers are all closer in temp to each other and the sci one is 2-3 degrees cooler, so now I have no idea which one to trust.

poke a thermometer in boiling/freezing water. if you have a thermometer that says its 95 degrees in boiling water, or 5 degrees in freezing water (or an icecube) then the thermometer is broken

actually that is not particularly accurate.

It is in very controlled applications but hard to do properly at home. Tap water contains all sorts of things that slightly alter the temperatures at which water boils. Ice water (water with a whole lot of ice in it, not a block of ice or near-frozen water) is frequently colder than 0 degrees as ice is colder when it is melting....

And if you plunge a glass thermometer into ice or boiling water you will probably break it well before it can register a temperature.

I have those ones from the supermarket that stick on the outside of the glass. I have one at each end of the tank and theyre pretty accurate. I double check with hubbys multi-meter every now and then. Those glass ones have given me grief with wrong readings.

Melting ice will be close enough to 0 C for calibrating a fish tank thermometer. And if it breaks from measuring the temp of a good cold drink, well it needed replacing anyway.

The cheap digital ones dont seem very accurate and their readings can vary with the battery voltage. I guess there is a reason they are cheap. The little glass ones with the plastic scale often aren't much better, I have seen ones where the scale rattles up and down inside the glass - thats REAL accurate. :roll:

I test mine against a good lab thermometer that we use for brewing and distilling, but even a cheap one of those will set you back $20 or more. But they are MUCH more accurate.

Those cheapies are OK to stick in the tank so you can see at a glance in there is a heater problem, but accuracy isn't theri strong point.

Cheers

Ian

The definition of 0°C is the temperature of a well stirred slush of water and ice at standard atmospheric pressure. Any normal day is going to be close enough for what we're doing. I don't think anything in tap water is going to make a significant difference, but you could collect rainwater and freeze it then make some slush out of that.

The problem is that you want something that gives a reasonably accurate reading around tank temperature rather than 0 or 100 deg C. I gave up on all of them years ago and invested in an electronic digital thermometer. Most aquarium thermostats would be lucky to maintain a temperature of plus or minus one degree and the temperature is not usually that critical anyway. It is only the fact that you are getting different readings that is throwing you off. You are welcome to borrow mine if you want to check yours against it.

That's interesting as my external with internal probe (black)Aqua1 above always reads much higher than the old school glass .. Like you it confused me so I added yet another of the glass ones from my daughters tank - and that too read different from it's matching mate ..

Not helpful when trying to check summer temp in an axolotl tank :-?

i'm not too fuss as about the temp, just annoys me that all 4 of them give me a different reading :roll: