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post #1 of 6 Old 06-02-2013, 01:06 PM Thread Starter
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Question tank too cold

I bought a 20 gallon tank and a submersible heater for 10-30 gallon tanks that is preset to 78 degrees. My temperature is 75 . Could this be due to lack of water current? If that is the case would an air stone help and should I place it directly below the heater to disperse the heat? Don't worry that my fish are freezing, I won't have any until next week-end.
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post #2 of 6 Old 06-02-2013, 01:24 PM
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Do you have a filter that you can place the heater by either in intake or output?

It could be due to poor current.. When I was setting my tank back up I plugged in the heater, but hadn't set up the new filter yet.. After a bit, air was reaching in the tank to put the plants in and there was this pocket of warm water around the heater and everywhere else was several degrees cooler. Once I turned on the heater though, I couldn't detect a change.
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post #3 of 6 Old 06-02-2013, 01:52 PM Thread Starter
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I moved my internal canister filter over the top of my heater and I'll see what that does.
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post #4 of 6 Old 06-02-2013, 02:42 PM
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I agree that the heater should always be close to the filter intake or outflow, which does help to circulate the heated water. But two other points need to be mentioned.

Heaters often operate at a slightly different temperature from that set. Example, if the heater is set for 77F, it may actually work to keep the water at 74F, or alternatively at 80F. Calibration is not exact for many heaters. Something to keep in mind until you get the tank at the temp you want.

Also, some thermometers are not accurate. The stick-on type often show higher temps than the ture temp.

Mention is not made of the fish intended, but we sometimes keep our tanks warmer than what is best anyway. 75F will suite a great many fish; some need more warmth.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #5 of 6 Old 06-02-2013, 04:37 PM
Also consider the ambient temperature of the room. What is it set to. Also note that glass aquariums are not great at retaining heat like acrylic aquariums. Other than that, as mentioned heaters are not perfect. A thermometer and a heater need to work in conjunction so you will need to find the sweet spot.

On the flip side of that, 75 is not really cold. Its just lower than your heater setting. Most tropical fish are fine at 72 to about 80. The best way to know if your fish/plants are okay it to check their profiles. If your tank is within range, your okay. You can always adjust your heater of coarse if your not satisfied. Just keep and eye on the tank after adjustments. You don't want to end up adjusting it too high.

Last edited by flight50; 06-02-2013 at 04:42 PM.
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post #6 of 6 Old 06-02-2013, 07:04 PM
Many of the relatively inexpensive Tetra heaters are set to 78 +/- 2 deg F. I have a couple (used to heat 5g water pails for water changes) that consistently deliver 75F.
You may need to invest in a better heater that you can adjust if you need 78+F in the tank.

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