# Can canister filters be placed at the same level as tank?



## hubbahubbahehe

Hi, I tried searching for the answer, but couldn't find it. I vaguely remember someone saying that you can't place the eheim canister filter right next to your tank cuz it will harm the motor and that canisters always go underneath the tank for that reason. I just want to run that by you and see what you think. Thanks.


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## GDominy

Canister filters rely on Gravity to help force the water through the canister.. the impeller is simply there to help it along.. By having the filter at the same level as the tank you no longer have the benefit of a syphon fed water source so the canister has to work much harder to get water through the unit.


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## Wasserpest

Man, I hate to disagree all the time :tongue: 

I really doubt that gravity plays a role in that. The weight of the water going down the pipe is completely offset by the weight of the water going up. Gravity would only help if the water would flow out onto the carpet. But canister filters are closed systems, and the water surface is on the same level for inlet and outlet hose.

I am not saying that it is okay to put the canister on the same level, but not for gravity reasons, but for problems priming it and getting any air out of it.

In any case, here is the discussion that we had a little while ago...
http://www.plantedtank.net/forums/showthread.php?t=5445


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## GDominy

Wasserpest said:


> Man, I hate to disagree all the time :tongue:
> 
> I really doubt that gravity plays a role in that. The weight of the water going down the pipe is completely offset by the weight of the water going up. Gravity would only help if the water would flow out onto the carpet. But canister filters are closed systems, and the water surface is on the same level for inlet and outlet hose.
> 
> I am not saying that it is okay to put the canister on the same level, but not for gravity reasons, but for problems priming it and getting any air out of it.
> 
> In any case, here is the discussion that we had a little while ago...
> http://www.plantedtank.net/forums/showthread.php?t=5445


Don't feel bad.. you actually added something to my argument ;-)

If you place the canister filter on the same level as the tank (asuming that the canister is same level as the water level..) The Canister then has to "Pull" the water up from the tank instead of allowing the Syphon to draw the water out.

Although Gravity does cancel out the net effects of hte syphon on teh return line.. this means that the impeller only has to apply enough force to the still water to keep it moving.. if the canister is above the syphon point then the impeller is doing a lot of extra work that would normally not be required.


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## cich

indeed... There is also a siphon on the output hose as well, making it equal. Raising the cannister will lessen the down-force on the in-hose, but also on the out hose, so it's the same performance. Also less water pressure, so less likelyhood of leaks.

--cich


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## wellbiz

Everyone makes great points, but I must question why then do the major canister filter manufacturers recommend placing the filter at least 24inches below the surface of the water? I am not an engineer and dont play one on tv either, but I would suspect there is a reason for this....

Jason


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## you

If your pump gets a tiny leak:

With the canister below the tank level the pump will still run and depending on the leak a siphon will start preventing the pump from airlocking.

With the canister above water level, the siphon can not start and the pump will eventually air-lock. This kills your pump from overtemp.


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## Daemonfly

I just recently moved my tank and the canister is now on the same surface as the tank itself. It was quite a PITA getting the air out and the "siphon" going, but after that, it worked quite well. I actually have more water flow now, most likely due to a huge reduction in head pressure.

It's true the pump gets a good gravity siphon reducing the force needed to get the water into the canister, but the pump still has to pump the water back UP the output. If it's too far below the tank, you won't get as good a flow (easily proveable).


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## GDominy

There is most defaintely a performance decrease based on the distance of the water path because despite the syphone creating a point of balance between teh inlet and outlet you are still fighting gravity to push the water up... This is not even close to the presure generated from moving water from a standing body at the same levels as the pump however (its not like calculating flow rate for a sump at all). Generally speaking you don't have to worry "too much" about distance from the surface of the water... I have a barely noticable performance difference (less then 50gph.. I measured) from 2-4 feet of distance from surface of the water using a Fluval 404.


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## kingkano

All I can add is that when I had my Fluval 304 on a tank where the water level was only a few inchs above the filter inlet hose, I had heck of a time getting the thing started. and even then I couldnt get all the air out of it. 

Soon as I moved the tank and the filter is now about 3ft below the water line it runs like a dream, the air expels itself all I do is plug it in.

Ken


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## kingborris

i run an eheim 2224 at tank level. that is, the base of the ehiem is sat on the same table as the base of the tank.

the filter works perfectly, with no apparent loss of flow, no leaks, nothing. 

HTH


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## macbrush

For me, as long as the impeller is lower than the water level things run fine, except that air don't get push out by siyphon as much as placing the canister under the tank. Apart from that, I found no difference.


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## Wasserpest

I can only repeat... no gravity involved after the filter is primed!

The longer the hoses, the more friction, the more the impeller/pump has to work to push water through. But it doesn't make the slightest difference if the canister is below, at, or above tank level.

Why do manufacturers suggest to place them below then? Because you can't get a siphon if the canister is placed above! Plus, usually ppl would want to place it into the stand anyway, so to avoid all of the "Can I place it in the stand, below the tank?" questions that's what they recommend.

Regarding the airleak, it really depends where the leak is, and again, totally independent from the placement of the canister. If the leak is before the impeller, the filter will airlock. If the leak is after the impeller, the carpet gets wet.

As long as the pump doesn't leak, and you get all of the air out, you can place it wherever. The longer the hoses, the more resistance, the less water comes out on the end.


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## GDominy

Wasserpest said:


> I can only repeat... no gravity involved after the filter is primed!


Incorrect.

If you manage to get a get a filter primed "above" the natural syphon point of the tank (regardless of height.. it doesnt matter, as you said) then the pump is pulling the water instead of moving the flow... This puts more strain on the motor. Canister filters are designed to operate below the syphon point.. Thats why Syphon Presure down = Verticle lift up.... If there is no syphon presure down.. then the canister is doing all the work.

Now.. In practice... It is very difficult to get a canister filter "above" the natural syphon point in a tank unless the impeller is above the water line.. as long as the water line is above the impeller then the canister will work just fine..


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## SCMurphy

As long as the canister is below the water level in the aquarium you should be fine. If you try to raise the canister above the water level in the aquarium you could run into a host of problems already mentioned. Runing the filter just below the level of the water in the tank, rather than 3 feet lower, will reduce the head loss on the pump and allow for close to the maximum flow rate. Someone could always experiment and start a filter at 3 feet down then pick it up to even, then try it above. I don't know how fast you can achive air lock but it might be interesting to find out, with someone else's filter.:wink:


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## kingborris

tried lifting my 2224 above the water level yesterday, and it didnt even cough once. no loss of output at all. 

would be a sod to prime up there though


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## NanoMax365

The gravity has little to do with it, it works on water pressure i think. Basically the intake will mostly always be below the outlet, its has to do with the water pressure difference between top and bottom of where the water goes into the filter, and where the water goes back in the tank. Try priming a filter with intake being above the outlet LOL unless its self priming it might not happen.


Wasserpest said:


> Man, I hate to disagree all the time <a href="http://www.plantedtank.net/forums/images/smilies/tongue.gif" border="0" alt="" title="Tongue" ></a>
> 
> I really doubt that gravity plays a role in that. The weight of the water going down the pipe is completely offset by the weight of the water 9going up. Gravity would only help if the water would flow out onto the carpet. But canister filters are closed systems, and the water surface is on the same level for inlet and outlet hose.
> 
> I am not saying that it is okay to put the canister on the same level, but not for gravity reasons, but for problems priming it and getting any air out of it.
> 
> In any case, here is the discussion that we had a little while ago...
> http://www.plantedtank.net/forums/showthread.php?t=5445





you said:


> If your pump gets a tiny leak:
> 
> With the canister below the tank level the pump will still run and depending on the leak a siphon will start preventing the pump from airlocking.
> 
> With the canister above water level, the siphon can not start and the pump will eventually air-lock. This kills your pump from overtemp.


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## natemcnutty

Sent from my Pixel 3 using Tapatalk


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## Surf

> I just recently moved my tank and the canister is now on the same surface as the tank itself. It was quite a PITA getting the air out and the "siphon" going, but after that, it worked quite well. I actually have more water flow now, most likely due to a huge reduction in head pressure.


Air lock is the heart of the problem. When you do a water change air can get in the system. The simple impeller pumps frequently used in aquarium products _cannot pump air_. If the airlock is not resolved the fricfion of the impeller on its shaft and the heat from the electricity the pump is consuming could cause the motor to overheat and fail. _Water flow through the pump is critical to cool the pump and to provide some lubrication_ for the impeller. 

This problem can also affect in tank filter with a pump . While on vacation one time I had more water evaporation than expected and water level fell below the level of the impeller in the pump. Air lock. When I got home the pump housing had melted and the impeller was effectively glued in place. I couldn't fix it and I had to make an emergency run to the fish store to get a replacement.


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## natemcnutty

If they haven't figured out the answer in 15 years, I highly doubt they're coming back here to check the thread 

Sent from my Pixel 3 using Tapatalk


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## xxxSHyXAxxx

Even if this is a dead thread it still is an interesting topic.

Generally the answer is no. You should have the canister below the tank. Technically? Yes as long as the majority of the water volume in the canister is below the water line. The type of pump in the vast majority if not all canister filters require gravity to assist with the flow down the filter inlet but as long as you can get a siphon going you're golden

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## nobaddog

natemcnutty said:


> If they haven't figured out the answer in 15 years, I highly doubt they're coming back here to check the thread
> 
> Sent from my Pixel 3 using Tapatalk


15 years later im here with the same questions. I welcome new ideas but the human race has become less intelligent so the answers from when we were smarter are welcome also. LOL


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## Bandit1200

Once the pump is fully primed and all the air is burped out, assuming you have a good seal it will not matter where you place the canister. As long as no air is introduced into the lines it will remain in balance, the weight of the water in both the intake and return lines is in equilibrium so a minimum amount of force is required for the motor to pump the water. Once air is introduced into the lines either from a leak or from maintenance on the canister, the equilibrium is broken and bad things can happen regardless of where the canister is located.


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## Streetwise

What happens during a power outage?


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## Bandit1200

Assuming both intake/return lines are completely immersed, nothing. Only the addition of air into the lines will break the equilibrium. Think of it like an elevator car and it's counterbalance. As long as the car and it's counterbalance are equal in weight, the motor to raise the elevator can be fairly small. It only needs to be large enough to overcome the friction of all the moving parts. If you cut the cable holding the counterbalance the motor is no longer strong enough to lift the car. The sealed intake/return lines work the same way, cutting the counterbalance would be equivalent to getting air in there. 



So as long as both lines remain below the waterline and no air gets in, they stay in balance.


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## HairyNoseWombat

> So as long as both lines remain below the waterline and no air gets in,


There is no reason the outlet/spray bar needs to remain underwater, even during a power outage siphon equilibrium will keep both hoses full of water as long as the intake/pickup is underwater and you canister will start working normally once power comes back.


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## Mkskid

Hi Guys, Great information!! Here's the ?. How do you Stop Airlock from happening? Going Below the waterline is Not an option. The Canister I have is a Fluval 307.


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## natemcnutty

Mkskid said:


> Hi Guys, Great information!! Here's the ?. How do you Stop Airlock from happening? Going Below the waterline is Not an option. The Canister I have is a Fluval 307.


You will want to look into a bleed valve or venturi loop.

Sent from my Pixel 3 using Tapatalk


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## HairyNoseWombat

> But it doesn't make the slightest difference if the canister is below, at, or above tank level.


The people that make canister filters know what they are talking about then they say it needs to be lower. By having the filter higher you are fighting against the laws of nature.


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## Somefishguy

Canister Head Pressure information:

Click below and for a good explanation Head Pressure and read the entire article here "Real World" Canister Filter Flow Rates:

https://www.aquarium-pond-answers.com/2011/09/head-pressure-in-aquarium-and-pond.html 

Here is an actual test using the Filstar S (manufactures rated at 250 gph) and timing its flow to fill a container. Note: -34% just plugging the unit in level with the aquarium and NO media!


Level with the aquarium - 164.53 gph
24" below the aquarium - 153.00 gph (-7%)
52" below the aquarium - 142.87 gph (-13%)

These results were with a filter with NO resistance in the filter (all media was removed). The tubing was not cut, shortened or lengthened (as tubing length can also change results by adding more water resistance).

What is noteworthy is that despite this siphon aid, tests and 1000s of practical use applications show that there is still a drop in flow rate for a closed system canister filter due to friction, tubing size, devices such as UV Sterilizers, CO2 equipment, etc. along with some impact from head pressure.
Another example is the Fluval FX6 with a 0 head pressure rating 925 gph, when in reality the typical head pressure flow rate is 600 gph or less after the added resistance in the filter media and tubing are applied (as well as the addition of a UV Sterilizer). 

Though it's far from an exact formula, a typical pump/canister filter flow rate with an under tank placement is about 50% to 60% of the published 0 head flow rate. This is the number you should use for mating your UV Sterilizer.


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## PlantedRich

Lots of high tech talk will miss the basics if we are not careful. Somebody mentioned it not being the gravity at all but the water pressure. What they failed to think through is WHAT creates the water pressure! The higher water column will always have higher pressure . 
But then for just the sake of ease of making the decision, we could actually accept that the filter folks who have been doing this for decades and longer will actually know what they are talking about. So when I want the real answer, I rarely go to a forum and ask rookies but check to see what the manual says first and then if I don't understand I may ask a forum!


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## Bunsen Honeydew

Not this again...


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## HairyNoseWombat

> Lots of high tech talk will miss the basics if we are not careful. Somebody mentioned it not being the gravity at all but the water pressure. What they failed to think through is WHAT creates the water pressure!


They obviously failed Science in school.


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