Heater Thermostat

  • #1
HI there,

First of all, let me say what a great site full of wealthy information and very knowledgeable people! Makes very good reading indeed!

Ok, lets get onto my problem as such....

Have recently bought a 2ft (60cm) tank which is a 10 gallon for tropical freshwater fish. It came with all the parts, submersible pump/filter, 150w heater, etc

I have managed to set the aquarium up, and it looks fine!

However, my problem is with the heater. I set the temperature on the dial to have it at 78F, waited a day or so for it to get to that temp, and it only ever reached 60F, which I read from the thermometer which I have on the opposite end of the tank from the heater.

So obviously I turned the dial up a bit to get it to the required temp read by the thermometer (don't really trust the dial readings on the heater).

My question is, is the light on the heater supposed to stay on UNTIL it reaches 78F then go off, or supposed to just go on and off like it has been doing? As I woke up this morning and the temp had dropped 6-8 degrees down to about 70F from the 78F I had it at. As that is what I thought a thermostat is supposed to do, is to monitor the water temp and go on and off accordingly to keep it at the desired temp.

Excuse my ramblings I think I make sense, and getting my problem across!

Or do I have a faulty heater?

By the way, there is no fish in the tank as yet, as I am not putting any fish in at all until this issue is sorted out.

Best regards to everyone

  • #2
Sounds like a bad heater. No way the tank should drop 8 degrees overnight. Especially considering that the 150watt heater in a 10 gallon tank is way overkill. That tank should never change more than a degree or two at the most.

If I were you, I would contact the manufacturer about getting a warranty exchange. Good luck!

  • #3
The light won't stay on until it gets to the final temp. It will turn on and off as the water temp is increasing. The heating element heats up the water and the heater. It actually heats up the heater more than the water and will cause the heater to shut off. That is ok as the water will cool down the heater and it will turn on again. That is why you have to wait so long for the temp to stabilize in the tank.

I don't believe those heaters with the temps on them. I would have a thermometer on the other end of the tank just like you. If you can turn up the heater dial and get the desired temp I think you would be ok. If you turn the temp control all the way up and it doesn't get the water to the temp you want you should replace it. I actually had a heater go bad and noticed it was bad by the light staying on.
  • Thread Starter
  • #4
Thanks for the replies.

I also thought that a 150w was a bit overkill when I first bought the setup myself. But seeing it came with it, thought I would use it to see how it went. Nothing to kill in the tank apart from a few plants

I did have a tank when I was a child, but my father set it up for me, so didn't really take much notice of anything besides the fish that was in it. I should have paid more attention of how things worked in it!

The temp has climbed (as I'm typing this) a bit back up to 76F from this morning where it was at around 70F so its definitely heating the tank for sure, but as for it stabilizing the temp, not sure, will have to wait another night I think, see what it does. As personally I think a 6 degree fluctuation (from what I have been reading!) is a bit much.

Failing that I do have another heater in the loft somewhere from many years ago, but it might be a bit big for the tank, not sure about the wattage, but its definitely bigger in size, so i'm assuming that the wattage is much higher.

Well the waiting game again proceeds...

Now off to read more of this great forum!
  • #5
The heater light will turn off once at acquired temp, Once the temp starts going back down, It will light up again.

Where did you happen to get your heater and what's its brand?

  • Thread Starter
  • #6
The heater came with the setup, it's a brand called "Heto".

Obviously I have never heard of it before, but someone else might have.


  • #7
Hmm, never heard of it either, But If the heater is fluctuating like that, Then I would go out and get another one like one of the marineland stealth pros.

  • #8

Is your filter running? It will circulate the water. That will help stabilize the temp throughout the tank.
  • Thread Starter
  • #9
Quick search with google about heater, says its some far eastern make.

Temp is 76-77F now, with heater light going on and off, lets see how the temp goes now, as the house heating has kicked in about 30 mins ago...so obviously the room will get a little warmer.

As for filter Mike, yes its running, can see it circulating the water from the top of the water going in a circle from side to side of tank, if that makes sense.
  • #10
Just a thought, what kind of thermometer are you using? One that sticks on the outside of the glass? Or a glass thermometer inside the aquarium suction cupped on the inside?

If it is the former, you may be getting a false reading from the outside glass being colder than the inside of the aquarium. I have both, and have noticed at times my sticker outside thermometer reads up to 2 degrees lower than the thermometer in the tank.


  • Thread Starter
  • #11
Just to add, temp ended up on 78F and stayed there for most of the evening with the house heating on, lets see what it is like in the morning.............

@ajpelz - It's a glass thermometer inside the tank opposite end to where the heater is.
  • #12
I use the Marineland Stealth Pros. and love them. I like the fact that I have a green light letting me know that the heater is on and a red light letting me know that the filter is heating. As for the thermometer goes I only use inside the tank thermometers because the paste on the outside of the tank thermometers are very inaccurate and hard to read most of the time.

Once your tank is up to temperature your heater should be able to keep the temperature within 2 degrees around the clock if it is of sufficient size and working properly. Heaters kick on and off normally to keep the water around it at a constant temperature. As the water circulates around the tank the water temperature varies a bit and the heater will kick on and off to adjust it.

As far as your heater being over kill, well in my opinion having an oversized heater is a lot better than having an undersized one. The more you allow the room temperature vary the more the heater will have to work. The larger heater should be able to keep up easier where a smaller one might not be able to keep up. The oversized heater will not have to work as hard and will last longer where an undersized one will have to work harder to keep the temperature constant which will shorten its life. I have even put two heaters in most of my larger tanks just for safety sake.
  • Thread Starter
  • #13
Thanks for the reply bowcrazy.

Just before I went to bed last night I checked the temp on the thermometer, it read a nice 78F, upon waking up this morning it read 76F which is a 2 degree drop, to which where it is now bordering on 76F.

I'm guessing this is an acceptable fluctuation in temperature? It's either the light on the tank when I put it on for a while which is altering the temp by 2 degrees or the room temperature. Although still haven't worked out why it dropped by 6 Degrees the other day though....

Although I will check for a few more days to see if stays like this, and hopefully it will. While sorting the heating issue problem out, the tank will be cycling anyway, so kill two birds with one stone so to speak!
  • #14
Could your thermometer be suspect. The stick to the glass on the outside of the tank type are very in-accurate.


  • Thread Starter
  • #15
Have an internal glass thermometer, staying around 78F now, very odd....

Also went and got the water checked today, water apparently ok to put starter fish in it, so put 2 danio and 2 platies.

However, after a week of the tank running, I'm not sure the water quality is fine, I will get a water checker myself and test it to be on the safe side....

Now to get some photos of Danios, oh fun fun, those guys shift!
  • #16
Testing your own water with a liquid test kit is alwasys the best way. Just remember if your doing water changes and using water conditioners like Prime you need to test prior to the water change and you must wait 24 hours after a water change to test again.

Conditioners like Prime will give you inacurate readings if you test right after a water change.
  • #17
I want to ask if the temperature on your heater setting matches the temperature on your thermometer?
I have two tanks, one 110 liter with 200watt juwel heater. I had to set heater on 28 to get 24-24.5 degree Celsius grade. The second tank is 94 liter with eheim 100 watt heater. The heater is set on 28 Celsius to achieve 24-25 Celsius.
I have multiple thermometers in both aquariums including digital thermometer to compare the thermometer readings and they are pretty much same.
Is it normal to set heaters on higher temperature to achieve desired temperature?
Thanks for any help
  • #18
Same here, I have a 50 gallon set to 81 degress but get 74. You just have to put the heater higher than what you want the temp to be


  • #19
Good. Thank you
  • #20
I have to set my heater at a lower temp in order to get the desired tank temp! My heater is set to 72 and my tank is currently at 76! I'm trying to get my tank to 75 right now for the happiness of the fish.
  • #21
Nope, The last few heaters have been surprisingly close, but generally, no ignore the settings on the heater, use a thermometer.
max h
  • #22
Most of the heater thermostats are a loose go by, mine are a couple of degrees off.


  • #23
I have the tank heater set at 84f and then added a thermostat that is set at 79f. Being the idea that the thermostat controls when the heater is on and off would you say this is more reliable than the thermostat built into the heater
  • #24
  • #25
The reliability is probably slightly better. Just curious why your tank heater is set to 84, what’re you keeping?
  • #26
I have mine set to 78. 84's going to overheat a lot of tropical and especially coldwater fish. Are you trying to breed some fish?
Its best to check by using a thermometer so the thermostat probably is better. Heater's can break. Normally the heater's for the smaller tanks are more likely to break and overheat. I prefer the Eheim brand.
  • #27
thanks for the advice I have the heat set high in the tank but the thermostat is set to turn the heater off at 79-78 the reason the heater is set high is to stop the heaters built in thermostat to turn it off so the other thermostat is in control

Basically its high so the heaters built in thermostat is not going to turn off and the heater on and off and the 78 is set on the thermostat

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