Thermometer reading vs. Heater reading?

[Gui101do]

I have a 55 gallon FW tank. Right now I have 2 kissing gourami, a featherfin catfish & an electric blue jack dempsey. Their temperature range is upper 70's.

I have 2 thermometers, one at each end of the tank. They both read around 82 degrees. My Marineland 300 watt heater is set to 76-77 degrees and the thermometer attached to it actually reads about 75 degrees.

Which reading do I take as fact? What's going on here?

 

[Greenmaster]

If the thermometers at the ends of the tank are submersible then I would say they the thermometers are right and your heater is toast. I would get 2 new ones... 150W because it's always safer to have 2 150w then 1 300w (if one fails then there is still heat... and if it fails the way you are saying then it's harder for it to cook your fish)

 

[mfdrookie516]

alot of times, heaters and thermometers dont read the same. mine is that way. i have a 300w marineland stealth pro in my 150g... i have the heater set on 76 but the temp of my tank is always 78. I'd say go off the two on the sides, and if it's consistent, dont worry about it

 

[Greenmaster]

Ya you could go that approach... turn your heater down a few degrees and monitor the temps closely.

 

[Gui101do]

The heater shouldn't be broken, it's only about a month old.

Well if the thermometers are correct & the heater's reading is wrong, then I should turn down the heater even more? Right now the heater is set to 76 & the thermometers read 81, so if I lower the heater to 74 or so, my temeprature should be about right.

 

[Greenmaster]

As long as it's not the sticky thermometers that are on the outside of the tank I would go with the thermometers. I would turn it down and watch temps closely, but first we should see if maybe it's something else that is the problem.
How is your water circulation?
What do you have for lights/other things that could heat the tank?
Is your tank close to a heat vent or a baseboard heater?
What is the temp of the room?
Is the tank near a sunny window?
Is there anything else that might affect the temperature?

 

[Gui101do]

They are two regular glass thermometers.

I have undergravel filter trays with two powerheads attached to the up-tubes. I have the powerheads pointed to spray from the corners towards the center of the tank.

I have a few plants in the tank, just some low-mid light things, so I keep the hood lamp on for around 6-8 hours a day. It's just the basic Marineland hood and bulb to fit across the 4 ft length.

Vents and windows are not near it. Room temp is low 70's.

 

[mgamer20o0]

sadly it seems the quility of the Marineland heaters been slipping. i know of a bunch of people with problems with them. go with the glass thermometers.

 

[Greenmaster]

But for now if you don't have the money (or don't want to spend it) I would go with mfdrookie561's suggestion and just turn the heater down 2-6 degrees till your thermometers read the temp that you would like in your tank.

 

[DragonFish71]

Or just go to Walmart and pick up a thermometer for very cheap. The glass ones are about 1.99.

 

[jsoong]

Glass thermometer (esp. the cheap ones) are not all accurate!! If you go look at the stack of thermometer at Wally's, they all read a different temp at the store, even when sitting at the same bin ....

You would want to use a high quality thermometer to take the temp before you junk your heater. A lab grade glass thermometer is of course the gold standard, but a good kitchen thermometer works as well. I use one of the instant read meat thermometer that can actually read down to 70. It is like $20, but gives accurate readings.

Depending on how the thermometer is made, you can calibrate it yourself. The standard lab calibration is: put in a cup of water with ice <let it equilibrate so there is both liquid water & ice>, and it should read 0C or 32F. Boiling water at sealevel should read 100C or 210F. <A bit less at altitude, you can find correction tables if you are up high.> You can then divide the 2 points into even intervals to find any temp accurately. Some thermometer don't have enough range to do this, then you have to calibrate to a known accurate thermometer. Most kitchen thermometer (even cheap ones) do have enough range for calibration, so is a better buy for your tank.

 

[DragonFish71]

The only trouble I've had with the Wallyworld ones vs the ones I get at a LFS are that they want to float sideways, the suction cups are for crap. As for accuracy, I have used both LFS and Wallyworld's in our tanks and they keep an accurate record. Our 10g that has fry in it has a sticky strip, a Wallyworld $1.99 special and a $3.49 Petsmart TopFin brand. All have the same reading. (I did that to make sure the temp was right before we stripped the fry and moved them to the 10 and never took them out) I agree that not all are accurate, there are variables due to a manufacturing error. But for the most part, the cheap ones do keep a pretty accurate temp.


That being said, I have heard nothing but good from people that use the digital ones. Maybe in the future that would be the route to take once you have the funds.

 

[dkpate]

I have my Stealth's set at 78*, but the temp is 80* in all tanks. I just assumed it was because the heaters are rated for more than the tank. *shrug* I had the thermometers from Walmart, and I threw them out (one broke when I was trying to move it, and I don't even think it's glass) because they were to off compared to the ones from PetSmart. I also have the sticky therm's on my tanks too LOL.

 

[Greenmaster]

A good way to test a thermometer is to crush up some ice and put it in clean cup (I usually put 20% ice.) with FW, stir it up and put it in the fridge with the thermometer in it... wait about 20 min take it out it should read 0C or 32F (the ice melts at 0/32 and the water wont freeze so the temp of the water will go down to 0/32 and stay there till all the ice is melted) it's the way a lot of companies calibrate/test their thermometers.

 

[Gui101do]

A lot of interesting responses...

As I've said, I have 2 glass thermometers, 1 brand new & 1 is from an old tank.

The glass thermometers are at separate ends of the tank and both currently read about 80-81 degrees.

My heater is currently set at 75 & the thermometer that is on the unit reads 74 degrees. It is only a few weeks old. I'm going to call my lfs & talk to my guy there, see if this is a relavent issue with this heater. I am still baffled.

 

[Greenmaster]

as I said I would test one of the thermometers and then adjust the temp based on the thermometers and ignore the temp on the heater.