Heating a 125 gallon tank

Currently, my 130 gallon tank is using an Ehiem submersible heater at 250 watts set to about 76 F for my ID sharks & plecos.

I was looking around for a decent price for a second heater for my new 125 G tank & come to find out that it's best to have 2 heaters for tanks this size.
Is that true?
My sharks & pleco are all nicely active.

So what are your thoughts and opinions?

I agree with this.
I have two heaters in most of my tanks just in case one of them fails, there is a backup one.
Why you need two heaters is also so the temperature is the same everywhere in the tank.

In general it takes about 3 to 5 watts per gallon. For 130g this would be about 390 to 650 watts. There are other online calculators that you can find to calculate wattage needed based upon tank dimensions and heat differential ( room temp vs desired temp ).

So based upon this rule of thumb, you are under heating with only 250 watts.

I agree that two or three heaters would be best, not only in case of catastrophic heater failure but also to spread heat across the tank water volume.

I have as well purchased heater controllers, they are extra insurance in case of failure.

Funny thing is, I'd been using a single 250 Ehiem heater on the 130 gallon tank for the last 3 or so years now. This tank was home to just the 15+ inch ID shark 1 12 in male pleco and some Oto cats.
It's now, for now, home to 3 ID sharks a second (female) pleco.
The 2 other IDs are now around 5 or 6 inches long & healthy looking. Temp is set between 75 and 80F.

In other words, one heater seems to do well.
The only bad thing they do is splash sometimes when they go to get some air.

Sandman1969 wrote:Funny thing is, I'd been using a single 250 Ehiem heater on the 130 gallon tank for the last 3 or so years now.
In other words, one heater seems to do well.

No problem. Rules of Thumb are meant as a guideline. If you are doing fine with the 250 Eheim then great ! I can perfectly rationalize that a 250 watt can run perfectly well if you maintain your home temp at 72 and your target is 76.

Gotta chime in on this one. Agree that 2 heaters provides a bit of insurance should one fail. Controllers should be used for multi heater usage. Disagree on the whole watt per gallon bunk. Depends on the brand and efficiency of the heater. I use Eheim Jagers exclusively, in particular the 300w 20in model. My CA/SA cichlids require temps of 80-84. I use 1 only 300w on tanks from 125 to 180g. I was originally curious as to whether it would cover a 180, and if it could, was it working too hard. I monitored the tank for a solid hour, and the heater had an actual run time of about 90 seconds. Putting heaters next to filter outflows makes them more efficient, spreads the warm water around. I use a single 150w Jager on 75 and 90g tanks. Again, no stress, water is always within a degree of the dial setting.

I had originally used a Marineland heater on the 130 with just the one ID shark. But that failed for unknown reasons. That's when I made the switch to Eheim.

Suprd, thanks for the idea of placing it near the outflow of the filter. I never thought of that.

Suprd71 wrote:Gotta chime in on this one. Disagree on the whole watt per gallon bunk. Depends on the brand and efficiency of the heater.

Completely agree on this . The 3 to 5 w rule is a guideline that the oldtimers use. Completely onboard that heater quality makes a difference.

I like to use more than one heater on my lager tanks to allow me to have a backup in case one fails.
Make sure your heaters are the "fail in Off position" so that a failure does not boil the tank.

Fail in off position?
I'm using an Eheim heater.

If a heater fails in an ON position the heating element stays ON and will possibly: heat the tank enough to kill everyting and in extream cases heat the tank and cause the glass to crack.

mikebike wrote:If a heater fails in an ON position the heating element stays ON and will possibly: heat the tank enough to kill everyting and in extream cases heat the tank and cause the glass to crack.

guess our tanks aren't oven safe......

I'm still confused about that fail in off position bit.
If it's in the off position, it's not powered, therefore not heating the tank. If it's not heating the tank, then it is not being used & should not be in the tank in the first place.