# [Wet Thumb Forum]-Eheim filter placement



## imported_timlawyer (Jul 14, 2003)

What is the optimum placement for the Eheim cannister filters? I know that they should be placed below the water line - but how far below? There is increased water flow on the intake by placing farther below the water line -but isn't that offset by the decreased water flow on the output by making the pump have to push the water higher?
Any thoughts?


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## imported_timlawyer (Jul 14, 2003)

What is the optimum placement for the Eheim cannister filters? I know that they should be placed below the water line - but how far below? There is increased water flow on the intake by placing farther below the water line -but isn't that offset by the decreased water flow on the output by making the pump have to push the water higher?
Any thoughts?


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## gpodio (Feb 4, 2004)

That sounds right to me, the pressure of the water going down would balance out the head pressure going back up meaning that if the canister is primed correctly, head pressure should be of little importance.

Giancarlo Podio


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## imported_timlawyer (Jul 14, 2003)

So if I had a choice between placing the filter 1 foot below the water line or 3 feet below the water line - which should I do?


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## anonapersona (Mar 11, 2004)

There is a maximum height allowed because when the filter is off, there is a full column of water pressing against the seals of the cansiter. If that height is too much the gaskets may leak.


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## nino (Oct 2, 2004)

Sorry but I have to disagree. They don't offset each other completely. If you buy an external water pump, many come with a chart and the gph will drop as they are placed further down. Look here : http://www.drsfostersmith.com/product/add_info.cfm?pCatId=4614

The intake/input is assisted by gravity (syphon effect) and the output works against gravity. If they cancel each other out totally, you don't need a pump. The water will just syphon down to the canister and go back up to the tank (assuming there is no media).


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## Alex (Mar 31, 2004)

If you have a choice, 1 foot would be better. Less strain on the pump and a little more flow.

Alex


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## gpodio (Feb 4, 2004)

> quote:
> 
> Originally posted by ninob:
> Sorry but I have to disagree. They don't offset each other completely. If you buy an external water pump, many come with a chart and the gph will drop as they are placed further down. Look here : http://www.drsfostersmith.com/product/add_info.cfm?pCatId=4614


Head height is always stated because most of these pumps are not used in closed circuits, rather in open sumps and refugiums where they have no back pressure at all to help them get the water back up to the tank. In a closed loop, overall pressure is the only concern as anonapersona pointed out.



> quote:
> 
> The intake/input is assisted by gravity (syphon effect) and the output works against gravity. If they cancel each other out totally, you don't need a pump. The water will just syphon down to the canister and go back up to the tank (assuming there is no media).


No it would just stay still as both would cancel eachother out. If head pressure was indeed an issue in closed loops, when you turn the pump off the water would automatically flow backwards. The pump has to obviously work against any obstruction or restriction such as filter media, bends and accessories. That's also why some quality canisters have a larger intake tube than output to avoid negative pressure inside the canister, specially if the pump is situated after the media.

Giancarlo Podio


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## nino (Oct 2, 2004)

Good point but are you saying that it doesn't make any difference whether you place a canister 10 feet under the tank compare to 1 foot under?


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