Confusion about heater placement in tank

[Splashes]

I just saw this on PetSmart's website:

"If you use a power filter or a canister filter with only one heater, place the heater at the opposite end of the tank from the filter. This will help ensure good distribution of the heated water.

Aquarium heaters come in different tube lengths to accommodate different height tanks. Because heat rises it is important that you pick the right length heater so that all the water is evenly heated."

I thought it best to place the heater *near* the canister filter so the waterflow would distribute the heat.

And what about the length? If you have a big tank, it will never span the entire length or height. ??

Any thoughts? Especially about the placement near or opposite the filter. Thanks!

[Rachel]

Splashes said:

I thought it best to place the heater *near* the canister filter so the water flow would distribute the heat.

I was under the impression this was the best placement as it moves the water and would help distribute the heat around the tank. How large of a tank are you working with?

And what about the length?

Not sure about this one. I would think the most important element would be getting the proper wattage for the size of your tank to provide it with the necessary temperature boost.

[Splashes]

My tank is only 2.5 gal, but the general rule was confusing. I have the heater on the side of the tank in front of the outflow of the filter (which is on the back, but the tank is not real wide).

[amanichen]

Oooh, I love being a mechanical engineer.

Without giving you a crash course in fluid dynamics and thermodynamics, I'll say that a heated tank will have the most uniform temperature distribution given the highest water turbulence. That is, if you let the water try to conduct the heat away, without mixing it, you'll have a pretty noticeable temperature difference between the volume around of the heater, and the rest of the tank. Dead zones don't heat as quickly as those which are actively being circulated.

As for where the heater should be?

It depends on a number of things, but you want it to be in a zone of circulation. Place it too far from the filter and you wont be putting it in a zone of circulation. Place it right next to the filter, and you're putting it in the path of turbulent flow which is going to mix with the surrounding water. It'll have a better effect, but it will still really only affect the zone of the water which is being actively circulated by the filter.

Placing the heater halfway between the filter and the boundary of the high-flow zone should yield the best results. If your filter is 1/4th of the way from one end, stick your heater at the halfway point in the tank, making sure that it's actually in an area where there's a steady flow of water past it.

Of course things like tank geometry, filter design, and any aquascaping will affect where the highest circulation zone is. You will want your thermometer to be as far away from your heater as is possible, that way you get an idea of the minimum temperature in the tank.

In small tanks you won't see much of a temperature gradient. Anything up to around 29 gallons won't suffer horribly unless you're really stupid with your heater placement, or don't have anything to circulate water for you =)

In taller and longer tanks (45H, 55, 90H, and 120 come to mind) you will probably want to run a powerhead, and two heaters, in addition to your filter. This is because it is very difficult for a single filter in one of these tanks to provide a large enough turbulent zone. Thus, you stick a powerhead roughly 1/4 of the way from the other end, and stick a heater near it. This will help provide a more uniform temperature distribution.

If you are using a canister filter, or a sump (especially one with an inline heater) you'll want the inflow and outflow to be as far apart as possible. On my tank I have the filter and heater outside of the actual tank, and to ensure good circulation I have to make sure that water comes in one extreme end end, and leaves through the other extreme end. Either that, or you want to use a air pumps and/or powerheads to help circulate dead zones in the tank.

Remember, you can also play tricks by using an air pump, which helps introduce oxygen, drive out carbon dioxide, AND provide water circulation in areas that might not see much.

[Splashes]

Thanks for all the great info amanichen! ;D

I'll have to do a better exammination of the water flow. The filter is a Whisper Micro set on the lowest setting so it doesn't bother the betta, so I don't really see the silk plant moving very far from the filter. The tank is a 2.5 gal Minibow, so it's not real wide or too long. I had the heater hanging on the side toward the front of the tank, and the filter is in the same corner on the back. Maybe I'll have to move the heater to the center back wall instead of in front of the outflow. But the silk plant covers the entire back of the tank. I'll also move the thermometer around to check for cooler areas. The thermometer is in the opposite corner of the heater currently.

Actually, now the heater and thermometer are in the hospital tank, although the water has remained at 76-77* without the heater even going on (weather warmed up again, but just in case). So you'll be happy to know Splashes is staying warm now! ;D

[amanichen]

Splashes said:

I'll have to do a better exammination of the water flow.

You won't need to. Your tank is so small you don't have to worry about it. Of the sizes I mentioned in my post above you don't really run into that problem till you hit 45+ gallons. I wouldn't worry about it.

So you'll be happy to know Splashes is staying warm now! ;D

I wish I could say I was happy, but I can say I'm less worried now