Water Temperature Question?

[sZENic]

Hello all, this is probably a silly questions but...

I have an aquarium thermometer that consistently says the water temperature is higher than what my water heater thinks. For example, if my heater is set to heat to 82F, the thermometer says the water is around 88F. But my heater is 'on' and heating when the thermometer says this. So I'm confused; because I thought the heater only heats when it's not the right temperature and turns off when it is.

I have a JW Fusion thermometer that sits in the tank using a magnet, and an aquatop 100watt heater. It's a 20L tank.

Do I need a new thermometer? Should I trust the thermometer? Is the heater wrong and I should set it lower than what I actually want?

Any help appreciated!

 

[N0body Of The Goat]

Some heaters are reknowned for having inaccurate thermostats, such as the Juwel ones eg. I have to set mine to 30C on the guage to get a thermometer reading of 24C.

I'd go by the thermometer reading if the water flow is reasonable going past the heater and the thermometer. Like I did when I saw the above anomoly, you could add a second thermometer termporarily for a second opinion.

 

[minnnt]

Some heaters are reknowned for having inaccurate thermostats, such as the Juwel ones eg. I have to set mine to 30C on the guage to get a thermometer reading of 24C.

I'd go by the thermometer reading if the water flow is reasonable going past the heater and the thermometer. Like I did when I saw the above anomoly, you could add a second thermometer termporarily for a second opinion.

Great advice! Heaters are rubbish at keeping the water at what you set them too, use a thermometer for a better reading and set your heater accordingly.

 

[ZoddyZod]

agree with the above......but what thermometer are you using? Some of these are innacurate as well. Is it alcohol, magnesium, digital or thermochromic ink?

 

[sZENic]

agree with the above......but what thermometer are you using? Some of these are innacurate as well. Is it alcohol, magnesium, digital or thermochromic ink?

Alright, so I got a second thermometer ("stainless steel thermometer"). It reads 86F while the old one still reads 88F... So should I trust this new one?

The old one is the JW fusion one i mentioned before, not sure what it uses. The packaging was incredibly brief in description.

 

[andyjw1]

Use a decent alcohol thermometer, do a quick check (depending on the range it has) by putting it in something you have a good idea of the temperature of like iced water, boiling water, fridge etc. Then use this in the tank.
As has been said, as long as the flow past both the heater and thermometer is good, then use the thermometer as your guide.

 

[sZENic]

Use a decent alcohol thermometer, do a quick check (depending on the range it has) by putting it in something you have a good idea of the temperature of like iced water, boiling water, fridge etc. Then use this in the tank.
As has been said, as long as the flow past both the heater and thermometer is good, then use the thermometer as your guide.

I placed both thermometers in the fridge for about 30mins. The fusion one read 46F and the stainless steel read 38F. I'm guessing there should not be such a huge discrepancy. How cold are fridges usually set to? I saw online it's usually 40F or below. So I'm thinking the stainless steel therm is the more accurate? Thoughts?

Could you tell me what thermometer you all use and works?