# External pump and canister filter



## leonroy (Sep 4, 2009)

With an external pump and canister filter is it better to 'pull' water through the filter or 'push' it into the filter?


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## nokturnalkid (Apr 3, 2007)

It's better to push water through the filter.


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## xGROMx (Sep 2, 2008)

Are you building one?


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## inkslinger (Dec 28, 2003)

Wet-Dry Filters you would "Pull" water thru with any kind of internal or external pump.
Canister filter like OC or Nu-Clear Filters you would like to "Push" water thru with a good High Pressure Pump.


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## deleted_user_7 (Jul 7, 2003)

I am glad you made this thread because I was considering using a pump to boost the flow on my eheim 2215. I was considering getting a 250 gph pump and just unplugging the filter and removing the imepeller. 

Basically you're asking if an external pump used to boost the flow/power should be put inline before the intake to push water through the canister and suck it from the intake tube or inline after the outflow to suck/ pull water through the filter, and push it up into the tank. 

The normal way a canister filter operates is essentially lie an inclosed sump. Water siphons from the intake and basically "falls" into the canister, and the pump on the outflow pushes the water back up into the tank. The wateriest sucked into the canister by the pump, only pushed out. 

I would think it would be safer to use an external pump on a canister filter (without the impeller or being plugged in) on the outflow to push water into the tank ( or pull water from the tank as well if it was powerful enough ) because i would be afraid the canister wouldn't stand up to the pressure if a powerful pump was used and would basically break the seal and leak water from the canister.

Just my thoughts... I don't know if my ideas are right or wrong. I was going to make a thread just like this!


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## Oreo (May 6, 2008)

The pump goes after the filter. This way the pump requires less cleaning and the bearing surfaces will last longer.

From a push vs. pull perspective on water pressure and the filter elements there is no difference as far as aquariums are concerned.


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## leonroy (Sep 4, 2009)

Lots of comments, lots of differing opinions.

Equipment in question: Eheim 2078 Filter + Iwaki MD-20R

Aquarium on the ground floor, filter and pump in the basement approximately 8 feet below the tank. Both pumps are on, the sequence of equipment is Aquarium > Eheim > UV > Iwaki > Aquarium.

At the moment the filter is under a *lot *of pressure (ie. if I turn the pumps off the thing starts dripping out of the seals). So justlikeapill I think you're right. If I pushed the water into the filter it'd probably burst.

Problem is, the pump cost a lot ($40 on ebay  and by creating backpressure on the intake it shortens its life; apparently most good pumps like pressure on the outlet?

In that case, what to do? The pump like pressure on the outlet...the Eheim can't handle the pressure...or can it?


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## Oreo (May 6, 2008)

As long as the pump isn't cavitating and has enough flow to keep the bearings cool your filter isn't causing it any problems.


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## leonroy (Sep 4, 2009)

Cool, I just bought an Iwaki MD-70RZ for fun...

I won't hook it up until I have a proper sump and Mazzei sorted out since with 70 feet of head and 42 PSI of pressure it'll probably blow my Eheim filter apart!

(The existing Iwaki MD-20R has 14 feet of head and 10 PSI of pressure)


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## billm90 (Jun 19, 2008)

justlikeapill said:


> I
> 
> I would think it would be safer to use an external pump on a canister filter (without the impeller or being plugged in) on the outflow to push water into the tank ( or pull water from the tank as well if it was powerful enough ) because i would be afraid the canister wouldn't stand up to the pressure if a powerful pump was used and would basically break the seal and leak water from the canister.
> 
> Just my thoughts... I don't know if my ideas are right or wrong. I was going to make a thread just like this!


I agree. a few more things to consider. a big pump forcing water into a plugged filter full of crud is going to put a lot of pressure somewhere. Right at the seal. Also if you put something like extra filter floss, or whatever for a run, you have increased pressure more. I have a rena so I can see how mine would fail. I dont know how your canistor is sealed.

I bet if you have a pressure gauge on the filter, working normal you would see nothing, maybe slightly negative due to the siphon. with a pump pushing in, very possitive pressure. Which would totally work against the design.

Pulling water out of the cansitor puts the restriction starting at the intake in the tank and all the way up to the inlet on the pump. It seems in my head a lot safer this way. no pressure trying to make plastic/rubber expand.

However I also feel if you went too big a pump pulling water out of the canistor, you will cavitate it, or suck crap out of the filter. You have to find a good balance on restriction, tube size, and pump size.

once you have that good balance. you may find yourself back to putting the stock impeller back in the filter, or you may get away with just needing a smaller pump pushing through as you wanted. (which I would be very worried about unless you play with the tank daily) 

Something else to take a look at. is your inlet to the cansitor bigger then the outlet? I know most have equal hose diameters, but the fittings? seems to me the outlet of the cansitor would be slightly smaller then the inlet, so the inlet would have an easier time free flowing (siphoning) into the cansitor vs the pumped side.
I thought the pump impeller would squeeze the water into a restricted outlet to create the pressure to push it?

If you want to pressurize a canistor filter, look at pool filters, or koi filters. My pool filter is pressurized, and has a fiberglass pill shaped container, with a 1" diameter O ring. That is clamped together with a metal ring that fits over both haves and is bolted tightly together. Manual says at over 50 PSI, it becomes a water rocker.

I also had a POS koi canistor filter that was similar to the pool filter mush smaller. It had a locking metal clamp that was very irritating to lock and unlock, but could take the pressure of the 600gph pump pushing through a 3/4" ID hose, maybe 5 feet long.


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## Sharkfood (May 2, 2010)

If you hit a point where you aren't getting good flow, and you're pulling water, you'll get starvation at the impeller which is very noisy, and I doubt it's good for the pump. The only real downside to pushing water through the canister is that leaks will be compounded by the positive pressure, but having leaks is generally a bad plan in the first place.


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## Oreo (May 6, 2008)

Sharkfood said:


> If you hit a point where you aren't getting good flow, and you're pulling water, you'll get starvation at the impeller which is very noisy, and I doubt it's good for the pump.


It's called "cavitation", and it's very bad for the pump.


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## leonroy (Sep 4, 2009)

billm90 said:


> I dont know how your canistor is sealed.


Eheim 2078. It has a square cross section with a huge foam type seal. It's not as safe as an O-Ring design IMHO.












billm90 said:


> Something else to take a look at. is your inlet to the cansitor bigger then the outlet? I know most have equal hose diameters, but the fittings? seems to me the outlet of the cansitor would be slightly smaller then the inlet, so the inlet would have an easier time free flowing (siphoning) into the cansitor vs the pumped side.
> I thought the pump impeller would squeeze the water into a restricted outlet to create the pressure to push it?


The filter appears to have equal sized openings as they go into the filter. I'd have to chase the path all the way through the filter to see if Eheim intentionally created a restriction for the reasons you suggest.



billm90 said:


> If you want to pressurize a canistor filter, look at pool filters, or koi filters. My pool filter is pressurized, and has a fiberglass pill shaped container, with a 1" diameter O ring. That is clamped together with a metal ring that fits over both haves and is bolted tightly together. Manual says at over 50 PSI, it becomes a water rocker.


If I aim for a sump design how would something like this compare with a decent canister?


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## billm90 (Jun 19, 2008)

leonroy said:


> If I aim for a sump design how would something like this compare with a decent canister?


 
I have a sump on my 100g planted tank with a rena canistor that is rated for 175 gallons.
the sump only gets turned on when I need to add water (fan cooling the lights evap lots of tank water) and right before lights out to add air to the water. I have ran the sump many ways and I find the canister filter is far better at getting all the fine stuff out of the water. After algae cleaning, or stirring up the gravel. 
The sump part works well for taking stuff off the surface of the water. Such as the white haze, or small pieces of plants. 
I have been going round and round in my head on some ideas for a sump that would work well on a planted tank. still working that out. The sumps generally will remove co2 from the water.

My 180 has a DIY dual sump (and large fish) with foam, filter floss, and fine filter floss. I want to add a cansitor to this tank as well since I feel it is better at trapping fine particles and for adding carbon to clean out the brown water the fish food adds. I have 2 return pumps on this set up and well as a refuguim. the sump returns add a lot more water current then I have ever seen a cansitor do.

I guess I like what both filters bring to the table. but really a cansitor works well on planted tanks.


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## bsmith (Jan 8, 2007)

I have an iwaki md10l on my XP1, prefilter. I inject co2 into the intake line before the iwaki. So it goes like this Tank>co2>Iwaki>Rena>Tank. I had a slight leak before but this was just due to a bad o-ring (4years using the canister as a reactor for the co2). I dont have the rena turned on unless I want to up the flow and clear up any debris from the tank faster.


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