What Size Heater

[Dandee]

What watt heater do I need for a 125 gallon? When I bought the aquarium, customer service said that two 200 watts would do the job. I don't think they are doing a good job. The heaters seem to be constantly trying to keep the temperature where it is set at. I have to mention also that the lid for the aquarium is still on order (they screwed up when this was all ordered and "misplaced" the lid). So could this be due to not having a lid on to help keep the heat in? The aquarium is still cycling so no fish in it.

This is the heaters I am using (two-200watt)

http://www.hagen.com/uk/aquatic/addinfo/fluvaleseries.cfm

[Namor]

Snazzy looking heater. :yes:

I believe the wattage per gallon guideline also depends on tank dimensions.

Perhaps this link could help.
http://www.users.globalnet.co.uk/~xeno/calculat.htm

I have also read that when using two heaters, they should be placed at opposite ends of the tank.

[Dandee]

Thanks for the reply.
I do have one at each end. I think what I might do is get another 200 watt and put it in the middle. This is a 6 foot long aquarium so it should make for more even heating with three heaters.

[CACAdmin]

I would say they ought to be adequate. I run one 200w heater in a 70g tank with no issues. It's quite normal for heaters to keep going on and off to maintain the set temperature. Staying on for a long time and then off for a long time would allow for much greater temperature fluctuations. I'd say you're seeing more temperature changes now without lids than you will with lids. Do you have lights on the tank or are they part of the missing lid/canopy? Lights also generate and help maintain heat.

[Dandee]

I have the lights but they need the lid to sit on. I was discussing it with the other half and we decided to wait until the lid arrives and try that for a couple days to see if it makes a big difference.

The heaters are on constantly without going off as they are not reaching the desired temperature (24.5C).

[GaryofMontreal]

Not having the lid on is extremely important for heat loss, and could be the problem. However, since you don't have fish in there, try turning one heater off and see what happens. Just because the unit is lit and reading doesn't mean it's working. If you only have one unit functioning, that could explain the difficulty. The older Hagen Tronic heaters had a way of looking on but not heating in a couple of my tanks, so maybe the new model has the same tendency.
With two 200 w ebo jaegers in a room of 19c, I am able to keep an easy 26.3 in my 125. I keep the heaters in the filtration outflow to move the heat and keep it from 'layering'.
The indicator lights are not on a lot. The only reason I have two is to prolong the life of the units - I was able to maintain this temperature when one died on me a while back for about two weeks with no problem.

[Very Scalare]

I bought one of these heaters a couple of months ago. It is forever flashing "LF" (low flow) no Tmatter where in the tank I have placed it. Temeprature readings are an issue as well, it will jump two oor three degrees and then back to it's normal temp in a minute or two. It has scared me on more than a few occasions. For the price of them I assumed they would be a tad bit more accurate than the one I purhcased has been.

[T Dawg]

The other factor is the room tempature.

My house is normaly 21c, so I have 500w to get to 24c in my 90g. When it gets closer to 20c in the house they are on more than they are off.

If you have funds to do so, another one is a great investment. If you have too much capacity they just do not go on. A 300 for the middle would also go a bit deeper and that may help conductive water flow

[OldMan]

I am presently heating a 120 gallon with a 250W and a 300W. They didn't have two the same size when I bought them. Those keep my tanks at a nice 24C all the time while I let the house temperature drop below 20C all winter. I would check as Gary suggested to make sure both heaters are working. If the lights are on all the time, you should be able to feel the heat by just bringing your hand close to a heater that size and noticing the warmer water.

[Dandee]

Thanks everyone for the replies.
I believe both heaters are working. They use to flash the LF (low flow) but I positioned them a little differently and they have not flashed LF since.

I'm going to wait until I get the lid and see how much of a difference that makes.