# Tank too hot with undergravel heater?



## krazzz (Oct 29, 2011)

Hello, I have a 90 gallon freshwater tank. I have had it set up for about a couple weeks now and I am running into a problem with the tank running too hot. I am using a 100w undergravel heater that was supposed to be for a 40 to 50 gallon tank. I also have two Fluval E200 heaters. For the first week I was using only the Fluval heaters and they were working great and the tank was only fluctuating about 1 degree. (always use two heaters in large tanks for more consistent heating and as added insurance in case one fails.) The tank has been hovering around 80 to 81 degrees. This week I plugged in the undergravel heater and the temp has now been about 83 to 84 degrees. I don't believe the Fluval heaters have turned on at all. Yesterday I unplugged one of them to see if that would help and it didn't. This morning I unplugged the other one and it is still at 83 to 84. I am very surprised that a 100w heater could keep a 90 gallon tank 84 degrees when my house is only 71. I guess I have 3 options:

1. Stop using the undergravel heater and going back to the two Fluval 200w heaters
2. Put the undergravel on a timer and run it two hours on and two hours off and use the two Fluval 200w heaters
3. Buy a rheostat and turn down the undergravel heater and use the two Fluval 200w heaters

What do you guys think is the best option? Does an undergravel heater help the plants that much? I'd rather just stop using it as that is the cheapest and easiest option. I've never used the undergravel heater before and I just don't trust it. I have a couple zebra danios in the tank right now to condition it but I need to get this figured out before I add more fish.


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## jschall (Apr 13, 2009)

krazzz said:


> Hello, I have a 90 gallon freshwater tank. I have had it set up for about a couple weeks now and I am running into a problem with the tank running too hot. I am using a 100w undergravel heater that was supposed to be for a 40 to 50 gallon tank. I also have two Fluval E200 heaters. For the first week I was using only the Fluval heaters and they were working great and the tank was only fluctuating about 1 degree. (always use two heaters in large tanks for more consistent heating and as added insurance in case one fails.) The tank has been hovering around 80 to 81 degrees. This week I plugged in the undergravel heater and the temp has now been about 83 to 84 degrees. I don't believe the Fluval heaters have turned on at all. Yesterday I unplugged one of them to see if that would help and it didn't. This morning I unplugged the other one and it is still at 83 to 84. I am very surprised that a 100w heater could keep a 90 gallon tank 84 degrees when my house is only 71. I guess I have 3 options:
> 
> 1. Stop using the undergravel heater and going back to the two Fluval 200w heaters
> 2. Put the undergravel on a timer and run it two hours on and two hours off and use the two Fluval 200w heaters
> ...


Get a controller and put it on the under-gravel, then set your in-tank heater to a slightly lower temperature so that the under-gravel heater comes on first.


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## krazzz (Oct 29, 2011)

Who makes a good controller? I have one for reptiles but I'm not sure if the temp probe is waterproof. Doesn't it seem strange that a 100w heater could cause a 90 gallon tank to get that hot? The heater was supposed to be rated for 40 to 50 gallon tanks. I am a little concerned that the substrate is too hot. What do you think?


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## DishyFishy (Aug 11, 2011)

If the two Fluval heaters were working why did you even turn on the undergravel filter? I would say just go back to those, sounds like the easiest thing you could do.


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## krazzz (Oct 29, 2011)

I added the undergravel heater to my setup because I wanted to go with a planted tank and my research showed the undergravel was beneficial to the plants. I read that the heat causes water (and thus nutrients) to flow through the substrate and to the roots. I didn't think that a 100w heater rated for 40g would cause such an increase in water temp. I have currently turned off the undergravel and went back to the submersibles. 

How many of you use an undergravel heater? Do you notice any difference vs. other heating options?


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## Willfull (Nov 9, 2011)

I have never used undergravel heaters but unless you have a temperature gradient between the upper and lower levels of the gravel nothing will flow. I suspect the flow with the gravel heater will be minimal.


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## Left C (Jun 14, 2005)

krazzz said:


> I added the undergravel heater to my setup because I wanted to go with a planted tank and my research showed the undergravel was beneficial to the plants. I read that the heat causes water (and thus nutrients) to flow through the substrate and to the roots. I didn't think that a 100w heater rated for 40g would cause such an increase in water temp. I have currently turned off the undergravel and went back to the submersibles.
> 
> How many of you use an undergravel heater? Do you notice any difference vs. other heating options?


I think that it was Dupla that came up with the idea that undergravel heaters were beneficial for the reasons that you mentioned in either the '80's or '90's. Peter Hiscock wrote about them in his 2003 book named Encyclopedia of Aquarium Plants. Along this time (give or take), undergravel heaters were being proved that they were of no real benefit. There are very few people that use them now. It is somewhat rare to even hear people speak of them. Anyway ...

What temperature do you want your aquarium to be? 76° to 78° or 80° to 81°?

What temperature do you have your Fluval heaters set on? 80° to 81°?

Your house is set on 71°.

Here is an idea. You could turn off the undergravel heater. Then set your Fluval heaters to 4° to 5° lower than what you want your aquarium to be. Let the temperature drop over a few days. The aquarium water has to get cooler since your house it at 71°. When the aquarium water reaches the temperature that you have the Fluval heaters set at, turn on the undergravel heater and let it run for a few days to stabilize. Then note what the aquarium water is after a few days. If this is a little lower than the ideal temperature that you want it to be, turn the Fluval heaters up a little bit and let the aquarium run like this for a few days again to let it stabilize. Then fine tune your adjustments as needed. I mention waiting a few days between adjustments because 90 gallons is quite a bit of water and temperature changes don't occur very quickly.

If you find that you need to put your undergravel heater on a timer, be sure to get one that is grounded, made for appliance use and is manually adjustable in 15 minute increments. Having the 15 minute adjustment intervals gives you enough room to fine tune your temperate setting. You can get a thermometer and push it down into the substrate to monitor the substrate's temperature. Also, have a thermometer to measure the temperature of the water column. Calibrate the thermometers before use.

Do my suggestion make sense?


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## ProjectCode858 (Nov 29, 2011)

I never find it ever being a problem because the water tends to always keep it cool. However, if the water is too cold and the heater is too hot, the temp difference could cause something.


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## krazzz (Oct 29, 2011)

I ended up going with a Blueline Biotherm Temperature Controller. I set the Fluval 2 degrees colder than the undergravel heater and the tank has been very stable. As far as I know the Fluval hasn't kicked on at all. The tank stays within one degree of what I have it set at. I'm very happy with the setup.


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