# Eheim next to aquarium, not under?



## Laith (Sep 4, 2004)

I'm looking at installing an aquarium in a location that doesn't easily allow putting an Eheim cannister under the tank.

I understand that the Eheim pumps in the cannister filters are made to push water, not pull. Therefore the water arrives in the cannister via siphon.

However, in the Eheim 2126 manual, it states to make sure that the top of the filter is at least 10cm (4") lower than the water level in the aquarium...

If this is the case, in theory I could put the filter next to the aquarium. Has anyone here tried that?


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## RTR (Oct 28, 2005)

Repeatedly. With reasonably clean, unkinked hoses (or those absurdly expensive external hose bends which absolutely must match the hose size, but which I stockpile) and care not to cut your hoses too short for ease of access when cleaning, I have no issues so long as I respect the 4" standard. I have even hedged on that at times, but self-purge of introduced air is severely hindered at less than 4" head differential, so I strongly urge keeping to that minimum difference.


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## Laith (Sep 4, 2004)

Great...

The fact that there's only a 10cm (in my case it would be more like 20cm, or almost 8") drop between the tank water surface and the top of the filter has no impact on the filter's turnover capacity? It doesn't lower the rated flow?

If that's the case, this would solve my issue!


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## JanS (Apr 14, 2004)

I've always kept my 2028 on the bottom of a stand next to the 125 it's filtering, and it works great. No loss of flow at all compared to another I keep directly under the tank it's filtering. You should be good to go.


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## RTR (Oct 28, 2005)

Eheims, as with most canister drives, are "pushers, not so good at "pulling". The closed system allows mostly gravity feed with a boost from the water itself, with the pump pushing the flow back to the tank at speed. So long as you are with their window of at least 4" and no greater head than xx inches (I forget the ranges), you should not see a great difference in flow unless you have a lot of excess tubing (friction losses).


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## Laith (Sep 4, 2004)

JanS said:


> I've always kept my 2028 on the bottom of a stand next to the 125 it's filtering, and it works great. No loss of flow at all compared to another I keep directly under the tank it's filtering. You should be good to go.


Jan - thanks. The question was related to the placement of the Eheim with regards to height. In this case the bottom of the Eheim will be level with the bottom of the aquarium, not down on the floor...

RTR - Yes, that's what I hoped. Sort of limits the size of the aquarium though. I was looking at a 125 gallon but then I'd need the 2128 which would be too high!

Maybe two smaller Eheims: a 2026 and a 2126...


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## Mellonman (Nov 2, 2005)

In my opinion, as long as you respect the 10cm drop, it's even better to put the Eheim filter next to the tank than under...

The output will even be better since there will be less water to push inside the tube and less friction losses.


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## RTR (Oct 28, 2005)

Mellonman has a good point, but I admit to having shot myself in the foot by minimizing tubing length before - it made filter cleaning a PITA. Amother lesson learned the hard way. For me, the "Baby Bear's porridge" length of tubing is just a bit more than it looks like I need at first setup.


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## Laith (Sep 4, 2004)

That is a good point; hadn't thought of that. And yes, I've been through the too short hose scene before as well!

If I do go for a tank volume where the 2x28 would be better than a 2x26, the height of the aquarium will be 60cm (23.6") so water level will be around 57cm (22.4"). The 2x28 height is given as 45.5cm (17.9"), and this is the height including the hose assembly.

So this should still work right? I mean the water level in the filter is probably around 42 - 43cm (16.5" - 17").

If not, are there any cannister filters out there that are made to pull and push water? I would imagine so...


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## RTR (Oct 28, 2005)

I believe that the differential applies to the top of the unit itself, not the hoses or to the water inside the filter chamber. The impeller housing is above the filter chamber. But I confess that I did not recheck any of the instruction booklets to confirm that guess - I've just always measured that way.


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## Phil Edwards (Jan 22, 2004)

Actually, when pushing water out of one end they're pulling it in through the other. The loss of water inside the chamber creates a pressure differential that pulls water in faster than gravity can pull it down. If you've ever tried a quick dump using a running canister vs. a gravity siphon you'll know what I mean. Basically what the impeller is doing is piling little portions of water into the outlet tube really quickly. The loss of water in that small portion leads to a localized low pressure which causes the surrounding water that's at higher pressure to move into the void which in turn gets piled up in the outlet and so on and so on. 

To get really geeky, water has a very high specific tension which acts as a sort of glue that holds the column of water together through some amazingly high suctions. Anyway, that tensile strength literally pulls a column of water down the tube vs. it just moving through the downdraft tube due to a gravimetric pressure differential. 

Man, I never in a million years thought that I would be applying this stuff to aquariums! LOL!!!! Thank you?


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## Laith (Sep 4, 2004)

That's great to know Phil! (I think?)  

Though I can't really figure out whether this re-inforces the notion that what I want to do will work well or whether it means that it may not be the best solution! 

It sounds like it means it is more than likely to work well?


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## RTR (Oct 28, 2005)

LOL! I was too chicken to detail, I just edged by it with the comment "...with a boost from the water itself" or somthing like that. There is a limit to how geeky I allow myself to be - it is pretty broad, but I do try.

To me it means that that your setup should work, Laith, and not significantly differently than a more conventionally placed canister. It may heat a tad less due to the better exposure than it would have inside an enclose cabinet as a small bonus. Eheims are low watt, so low heat gain, units, but when you use as many as I do, it becomes non-trivial.


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