View Full Version : one or two heaters in 125 gallon

08-02-2010, 02:29 PM
o.k. guys, I am overwhelmed and need some advise from the specialists here at the forum.
I still have to buy a heater(s) for my 125 gallon. Should I put a higher watt heater in the middle or two on each side and what watt do I need?

08-02-2010, 03:05 PM
Are you having problems controlling the temp?I recommend two only when you are having trouble maintaining a constant decent temp.
I have one heater in my 135 and its always at 79 degrees in the Winter months.
Right now with the heater off its 81 in there.

08-02-2010, 03:23 PM
It is my brand new 125 gallon and I want to buy a heater early next month, have no experience at all with that set-up. Should I get than a 500 watt filter, or what do you have?

08-02-2010, 04:31 PM
Two heaters are always recommended for larger tanks. The wattage depends on the number of degrees you want to raise the temp over your average room temperature. Two heaters will heat the tank more evenly, prevent a large temperature drop if one were to stop working, and last longer due to not having to work as hard. I would recommend two heaters of at least 300 watts for that size tank, and if it were my tank I would use two 400 watt heaters just because I like to make sure I have more than enough. I use two 300 watt heaters on my 90g and have no problem maintaining a constant temperature everywhere in the tank.

I keep my house at 73 in the summer and 68 in the winter. The tank I keep at 82.

08-02-2010, 05:28 PM
I always recommend especially for larger tanks In-Line heaters. This is basically because for large tanks most people use canister filtration...and these In-Line style heaters are MUCH more efficient at heating your tank than a standard heater that just kind of sits there and heats the water around it. The water is ran through the inlines and dispersed back into the tank. I use 2 200watt Hydor ETH heaters on my 150G, they also have the added benefit of keeping your tank neater in appearance. If you werent going with a couple of canisters for the tank Rena makes a heater that replaces the intake strainer of most filters...which has about the same principle. The benefit of this style of heating is that your tank remains a consistant temperature without warm/cold spots, which is especially important when dealing with a 6ft tank :22:

08-02-2010, 05:37 PM
I don't need the heaters thru the summer, because I have my AC set on F81 and in the winter on 65 (but have a gas fireplace in the familyroom where the big tank is). I think I go with two heaters. Still have to do my homework on that In-Line heaters. Does Foster & Smith hase them? Or who else sells them online? Should I also get two 200 watt? Are they much more expensive than the other ones?

08-02-2010, 05:42 PM
Sorry, forgot the mention the fish which get in the tank. My common pleco, 6 clownloaches. Right now I only have 3 large female swordtails, a small rainbowshark and 2 small giant black upside down asian catfishes in it. I still will get probably rainbowfish or large tetras later. I guess a temperature of 78 would be o.k. in the winter.

08-02-2010, 08:33 PM
For reference, I have two 250 watt heater in my 125 and the temp is very steady.

08-02-2010, 09:05 PM
I have a single 300W heater in my 125, and the same in my 225, and it stays constant, however I also have a lot of water movement.

08-02-2010, 10:32 PM
Foster and Smith does sell them and they are usually about twice the price of a standard aquarium heater of similar wattage. You would also need to run 2 canister filters to use the In-Lines. Which for a tank of that size is normal filtration anyway. Just do a search for Hydor ETH heaters and you should be able to find all sorts of websites that carry them.

08-02-2010, 11:40 PM
I have two Fluval 405 running, so guess I am a candidat for that set-up. Just have to plea to my hubby to spend some more money on it!

08-03-2010, 12:02 AM
It's been my experience that heaters are the the weakest link in the equipment chain, ergo the most likely to fail. With a large tank like 125g it will take longer for a failed heater to cause harm (than say in a 20 gallon), on the other hand, it is harder to recover once the tank loses it's temp. Given those realities, I've always used 2 heaters when I was running tanks over 75g - mostly to ensure against heaters failing in the off position. It doesn't protect against failing in the on position, but doesn't make an 'on' faliure situation worse either.

08-03-2010, 12:17 AM
I definitly get two. Better safe than sorry! Just don't know yet if I can afford the expensive ones. Like to have some money left over for plants and fish!