# External filter positioning....



## JohnC (15 Dec 2012)

Hi,

External filters are designed to be placed below the tank as most of them use gravity and a syphon effect to help move water around in some way. Unfortunately this new tank i'm helping update only has a spot for the external filter, it really needs refitting, next too and spanning the water line.

ie half below and half above the upper water line of the tank.

according to the owners the external on it has "worked for a day after the previous guy came then stopped working while becoming very noisy". I'm presuming that water has drained out of the filter once the intake has breached the surface and air has come back into the head stopping the suction, water in the filter draining back into the tank.....

Obviously this can lead to motor burn out in the long run and other problems, which is why they don't recommend externals being above the tank height...

Lacking space and working with the equipment they have what do you guys think of either -

With the external still where it is (bridging the top of the tank) refitting the outputs to a position lower down the water column so they would never risk exposure to the air? do the trick without too much risk?

Second plan, as there is an additional hydor pump in the tank, using that inline to push water into the intake or draw water through the outtake there by offsetting the lesser gravity effect of the filters position? and if so which would be a better position for the pump, forcing water into the intake or drawing it out of the outtake?

Opinions sought.

Thanks in advance,
John


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## krazypara3165 (15 Dec 2012)

This is just using my limited knowledge of physics, but...even If the filter relys on the syphon effect, I would imagine it would still be ok above the water line as it would still have the syphon effect, just in reverse. E.g instead of the water falling down the intake pipe which in turn creates the syphon effect pushing the water back upto the tank if the filter was above the water line it will 'fall' down the outlet pipe creating the effect that helps pull the water up the inlet. The only problem would be that it puts more strain on the pump to initially prime. But as I said this is just baised on my limited knowledge of physics.....


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## foxfish (15 Dec 2012)

I cant see that would ever work successfully, you will just be forever getting air locks, the impeller needs to be below the tanks water level.
The only way to make a canister filter above the water line would be to pump water in to the canister - not pump out.
You could use a pwerhead inside the tank to push water into the canister & remove the impeller from the canister powerhead.


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## Antipofish (15 Dec 2012)

Foxfish is right. It wont work well if at all.


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## JohnC (15 Dec 2012)

foxfish said:
			
		

> I cant see that would ever work successfully, you will just be forever getting air locks, the impeller needs to be below the tanks water level.
> The only way to make a canister filter above the water line would be to pump water in to the canister - not pump out.
> You could use a pwerhead inside the tank to push water into the canister & remove the impeller from the canister powerhead.




Well....

Kinda. It's not fully above the water. From what i've read elsewhere the airlocks and hassles come from the outflow being above the water or being allowed to let air back in to the head. If this is avoided then the only issue with air getting in is from leaks or bubbles in the tank itself (this shouldn't be a problem in this tank) since it is a closed system.

I presume smaller bubbles that do sneak in should be forced out again by the water movement eventually.....

Hence my thought on adding the extra oompf of a power head in line to make sure there will always be additional flow going through.

But then, like you mention it is almost just better to leave the pump in line. I think however the pump isnt a strong as the filter..... hmm

I presume with the pump inline with the filter it would be best to run similar ratings of flow otherwise one or the other of the units will be spinning faster then it was designed to go. Not being an expert on impeller motors would this put an extra strain on the motor or actually avoid strain on it by "helping it along"?


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## JohnC (15 Dec 2012)

foxfish said:
			
		

> I cant see that would ever work successfully, you will just be forever getting air locks, the impeller needs to be below the tanks water level.
> The only way to make a canister filter above the water line would be to pump water in to the canister - not pump out.
> You could use a pwerhead inside the tank to push water into the canister & remove the impeller from the canister powerhead.




Well....

Kinda. It's not fully above the water. From what i've read elsewhere the airlocks and hassles come from the outflow being above the water or being allowed to let air back in to the head. If this is avoided then the only issue with air getting in is from leaks or bubbles in the tank itself (this shouldn't be a problem in this tank) since it is a closed system.

I presume smaller bubbles that do sneak in should be forced out again by the water movement eventually.....

Hence my thought on adding the extra oompf of a power head in line to make sure there will always be additional flow going through.

But then, like you mention it is almost just better to leave the pump in line, remove the impeller and turn the filter off. I think however the pump isnt a strong as the filter..... hmm

I presume with the pump inline with the filter it would be best to run similar ratings of flow otherwise one or the other of the units will be spinning faster then it was designed to go. Not being an expert on impeller motors would this put an extra strain on the motor or actually avoid strain on it by "helping it along"?


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## JohnC (15 Dec 2012)

obviously to prime the filter i'd have to start it lower then the tank top or do some crazy self priming.


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## JohnC (16 Dec 2012)

on testing i've discovered the impeller is snapped, there is a leak in a valve on the top, the fuse was blown which indicates it probably ran dry then overheated. Overall i don't think it's worth finding the part to try and repair.

But i can use a powerhead in the tank to run water through the camber as discussed to get the benefits of the filtration at least. So it does solve the problem in the end.


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