Don't Know Which To Trust

[K.J.]

I have a thermometer mixup!

Thermometer A is a kitchen meat thermometer
Thermometer B is a mercury fishtank metal one
Thermometer C is one you put outside to read the temperature.

Of those three, A would probably be most accurate. However, I have a 10g tank that's supposed to be fore breeding bettas. It's got a typical TOPFIN heater in it, set to the lowest notch. But the temperature reads 85+ on A! Whereas B marks it a perfect 85F.
When C reads 31F, A reads 43F. So, I'm not sure which is right. My other 10G has a heater and is almost the same 85F. Who would be right?

 

[rdd1952]

I would tend to trust B. The meat thermometer would, IMO, be flawed as it would normally be used for much higher temperatures. And most outside thermometers are not very accurate.

 

[K.J.]

Are the stickon thermometers accurate? It's a breeding tank, so obviously I can't have a fluctuating temperature.

 

[Colin_T]

Kitchen/ cooking thermometers are accurate for high temperatures but not very good at low temps. They are designed for taking the temp of cooked food.
The outside thermometer should be pretty accurate but it depends on the quality.
I would trust the fish tank one for a fish tank. If you are concerned it isn't accurate take it to your LFS and compare it to the ones in the shop. Just ask the shop assistant if you can compare your thermometer to some of theirs, as you are worried it might be inaccurate. Put yours and a couple of new ones next to each other on the counter for a couple of minutes and see if they match up.

The stick-on thermometers are not as accurate as internal ones. They read the air temp and not the water temp. This can cause them to be out a tiny bit. The liquid crystal display can also be damaged quite easily and give you false readings.

 

[rdd1952]

I'm not certain how accurate they are. Even the digital ones are spotty. I have 4 of the Coralife digitals and if I put them all in the same tank, I get readings that vary by as much as a degree and a half. As long as your heater is functioning properly, you shouldn't see any swings that would be harmful. I don't think the actual readings on the thermometers is as important as the high and low readings you get on any one of them. That will tell you how much swing you are getting.

 

[loachman]

In general, expect at least an error of +/- 1 degree on all thermometers under $30. More money, and you'll get a bit more accuracy but it's not really that big a deal. If you're within a degree, you're close enough for your fish.

The meat thermometer is probably the least accurate, since it's calibrated for higher temperatures.

 

[TwoTankAmin]

I have used all kinds of tank thermometers from the stainles steel hang ons to floaters, suction cupped to glass ones, corallife digitals (had the same issues as mentioned above) and even priey wireless digitals. I dont trust any of them to be really accurate.

Tank temps will vary some, but then so do water temps in the wild. If you are close, you will be fine. I have had an awful lot of fish breed in my tanks and have yet to see any of them reading the thremometer