# Can't get aquarium temp down



## drew27c (Dec 7, 2016)

I have a 75 gallon that I cannot seem to get down below 79 degrees. Previously I had an Eheim 300W, and I replaced it with a brand new Aqueon 300W. Even on the lowest setting the temp will not drop to where i want it at 75. This is the wattage needed for my size of tank, so I cannot understand why this is happening. Help!


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## Deeda (Oct 12, 2012)

Is the only thing that has changed is the new heater?

Did you place the new heater in the exact same spot as the old one?

Does the new heater have a light that shows when it is on? If so, check to see if it ever turns off, it is possible to get a defective unit right out of the box.


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## noddy (Nov 20, 2006)

Does the temp drop if it's unplugged?

P.S, I have a 300w heater on my 210g tank. I only had a 250w heater on it until recently.


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## Narwhal72 (Sep 26, 2006)

What is the ambient air temperature in the house and what is the tank temp with the heater unplugged?

Heaters can only raise water temp. They can't lower it below whatever the ambient air + other heat sources (pumps and lights) make it.

Andy


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## tanker3 (May 18, 2015)

Agree with all. Unplug the heater and monitor for a few hours.


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## drew27c (Dec 7, 2016)

Hey folks. Yeah I have unplugged in the past and the temp goes down. The room temp is always 68. I put the heater in the same spot as the previous Eheim. I am going to move it to a different area of the tank to test. Nothing else has changed. I'll report back. Thanks for the insight!


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## noddy (Nov 20, 2006)

Sounds like it's faulty to me. I'd send it back.


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## drew27c (Dec 7, 2016)

Two faulty heaters in a row?


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## wryan (Dec 6, 2015)

drew27c said:


> Two faulty heaters in a row?


Which two heaters were "faulty" ... the Eheim and the Aqueon ?

Or two Aqueons ?

If it's two different brands, I'd say that's fairly unlikely ...

In any event, have you looked for an external source of the problem ... like say, being in the outflow path of a warm air duct of your home heating system ?


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## noddy (Nov 20, 2006)

wryan said:


> drew27c said:
> 
> 
> > Two faulty heaters in a row?
> ...


That's why I asked if the temp goes down when he unplugs the heater.
If the room is always 68 and the Eheim kept the tank at 75, either the new heater is faulty or is just to large for the tank.
My 210 is in a room that is 68f and it's kept at 78f by a 250w heater.
I personally wouldn't put anything larger than a 150w heater on a 75g tank.


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## tanker3 (May 18, 2015)

Can you not set the temp lower? I do not use the temp on the heater. I use the number only as a reference, or as a starting point and adjust accordingly.


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## wryan (Dec 6, 2015)

noddy said:


> That's why I asked if the temp goes down when he unplugs the heater.


Doh ... failure to keep the entirety of the thread in mind - including your question and his answer to it - when I replied ... :roll:



noddy said:


> If the room is always 68 and the Eheim kept the tank at 75, either the new heater is faulty or is just to large for the tank.


Makes sense.



noddy said:


> My 210 is in a room that is 68f and it's kept at 78f by a 250w heater.


Amazing how well that water holds it's heat ...



noddy said:


> I personally wouldn't put anything larger than a 150w heater on a 75g tank.


 :thumb:

I have 150w Eheim on the 55g in the living room ... box sez "For tanks 53 - 79 gallons" IIRC.

Has no problem keeping the 55g tank @ 78 - 80 ... runs very little in the winter, as compared to the summer when the difference in the ambient air temp is greater. Even then it doesn't run all that much.


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## wryan (Dec 6, 2015)

Next question: _By what means is the temperature measurement being taken ?_


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## Narwhal72 (Sep 26, 2006)

I would still unplug the heater and monitor the tank over the next 24 hours. It should cool down to just above room temperature. Pumps and lights contribute some heat to the system which typically brings the water up a couple degrees above ambient.

If the tank is situated near a furnace vent it could be warmer than the room temperature.

Also I would check the thermometer to make sure it is reading properly. Checking the room temperature with a separate thermometer is also a good idea.

Andy


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## Aquariguns (Jan 15, 2015)

That heater is way too much for that tank size and ambient air temp as others stated. i am using an Eheim Jager 250 on my 125 with similar home temp. According to calculations, a 150-200 would suit your tank and temp requirements.


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## newcichlidiot (Jul 7, 2010)

300 watts seems like a lot of heater, go with [email protected] watts each. $.02.


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## BuckeyeTez (May 10, 2016)

Or buy a temp controller and never worry about it again. My inkbird was $35 and keeps my temp 76-77* and will alarm you if it gets too hot or cold.


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## drew27c (Dec 7, 2016)

I have a digital and manual thermometer. I'll scale down the wattage on the heater, as I've exhausted all other possibilities.


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## Narwhal72 (Sep 26, 2006)

The wattage of the heater means absolutely nothing in this situation. Both heaters are thermostatically controlled. The thermostat will turn off the heater when it reaches the desired setpoint. The only difference between a higher wattage and lower wattage heater is how long it takes to get up to temperature and how long the heater has to run to maintain the temperature. A higher wattage heater will have a shorter cycle time.

Other than a defective heater which is stuck on all the time (unlikely as the tank would be up in the 90's by now) there are ONLY two possibilities.

1. The heater thermostat is not calibrated properly. To reset the calibration, take the set temperature of the heater and subtract it from the actual temperature of the aquarium. Then turn the heater down the difference. This will recalibrate the heater. Then you can set the heater to the desired temperature with the proper correlation.

2. Outside heat sources are contributing heat to the system. In which case, the heater may not be contributing any heat to the system as the thermostat should be shutting the heater down if the tank temp is higher than the setpoint.

I still think #2 is the most likely suspect and I have previously said how to check for that.

Andy


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