Question regarding canister flow rate w/inline accesories


Junior Poster
Feb 2, 2010
I have read that I should shoot for a 10X per hour turnover rate when purchasing a canister filter.

I will have a 33 gallon tank so I was trying to find an Eheim in the ~330gal/hr range and I ran across the Pro3 2075 (G160). Its dimensions are approx 1 foot by 1foot and 1.5 foot tall. I have never had a canister filter before and that seems HUGE to me.

Surely en external canister filter doesn't need to take up that much room under my stand and be nearly as tall as the tank is to do its job ?!? The canister filter and co2 tank will take up all the space under my stand ! :(

So that got me to wondering about the 10x turn-over rule of thumb I have been seeing. Am I misunderstanding something here? Is that just something to aim for because filter manufacturers will trump up their rating and what they say is a 300 gal/hr filter is actually more like 200Gal/hr ?

And I said all that to say this.....

What happens if you plumb in an external in-line heater and an in-line co2 reactor? Does that decrease the flow even more?

I am not trying to go cheap here and I am not opposed to spending the money for a good filter that is going to last. But it seems that a filter that is actually going to do a 10x turnover of the tank volume is going to be huge in size. And 2 smaller filters would probably take up more room under the stand.

Help me out here.....I must be mis-understanding something.

Anybody else have a planted 30 gal tank and Eheim filter? What do you use to achieve 10x turnover rate?



Plant Guru Team
Lifetime Member
Sep 23, 2007
South Florida
Hi Bill,

Think about the 10x as a rule of thumb for OVERALL need of flow.


You need flow for filtration.
You need flow for the c02 r eactor.
You need flow for the heater.
You need flow to overcome friction and head pressure.
You need flow to provide current for the fish and plants.

When you want to run ALL of this off one filter, yes it can be huge in gph requirement.

Remember that each component UPSTREAM of the filter outlet will reduce the flow and increase the pressure the canister has to deal with. Combined with usually 1/2 or 5/8 tubing this is a disaster.

I do think that most flow estimate are overly generous.

You may want to just run the filter and heater off the canister. Figure out another method to drive the reactor and simply flow the output to the tank. Use another pump just for the reactor and some flow.

Oversize your tubing when possible to increase total flow. Thin tube flows less volume at a faster rate. Bigger tubing flows more water at a lower rate.


Lifetime Charter Member
Lifetime Member
Jan 15, 2009
Most filters are rated with no media in them. In most cases you can assume the flow is half that when full of media. Eheim seems a little better with their cannisters and I've read 70%. For things like wet/dry filters 3-5x turnover is fine. So the actual filtration part of it is not so great. You can then supplement the flow with things like a Koralia pump to get to your 10x+. I would not recommend putting your CO2 reactor on the same leg as the filter because as it clogs you will affect flow through the reactor and you'll have weird CO2 issues when you "know" you have enough. It may be better to put the external heater and reactor on a separate leg.



Junior Poster
Feb 2, 2010
OK I think what you all are telling me is that the 10x rule is not how much water gets run through the filter .....but rather how much water is being moved per hour.

So if I want to achieve 10x turnover per hour on a 33 gal tank (i.e. 330gal/hr)......then I could use a canister filter that ran 165 gal/hr through the filter and then get a power head or Korilia pump or something that had a 165 gal/hr rate that just moved water around inside the tank? I assume the idea here is to have no dead spots anywhere in the tank as I would think in a planted aquarium the only thing the filter is used for is just for mechanical filtration.

But when you all say run the reactor on a separate leg.....what exactly do you mean?

I assume you mean run the output of the canister filter into an in-line heater and then the output from the heater into a spray bar or lily pipe back into the tank. But that I would also need to buy an external pump that pulls water out of the tank and drives it through a CO2 reactor and then back into the tank. Is that what you meant?

I guess I should have stated that I was trying to keep as many things out of the tank as I could and keep them hidden under the stand.

The reason I am giving this so much thought right now is that I plan to build my stand here in the next few weeks and I want to be sure I have enough room under there to accommodate all the components without it being too cramped.

So as always....any guidance will be greatly appreciated.



Guru Class Expert
May 23, 2009
My DIY CO2 reactor contains nothing, so it won't get clogged.
Its openings are larger than the hose of the canister filter connected to it.
I have to use clamps to connect the larger hoses to the smaller ones.
So the flow is not reduced much.