So what you are saying is you have a canister that is twice the size of your tank? I do not think this is the case. Perhaps you could rephrase your question. You might also want to look up sump filtration on Google. That is the normal method for doing what you describe, but it is normally used for larger tanks and mosrlt for sw. However, fw sumps are used on bigger tanks as well.
But I run canisters on a few tanks, none of these holds much more than a couple of gallons. Here is are examples from Eheim:
EHEIM professionel 3 250
EAN 4011708202562
Article No. 2071020
UPC (-)
For aquariums of about. 120.00 l
For aquariums up to approx. 250.00 l
Pump power (50 Hz) per hour of approx. 950.00 l
Pumping head approx. (H max at 50 Hz) 1.50 m
Power(50 Hz) to 12 watt
Filter volume 3.00 l
Pre filter volume 0.50 l
Container volume 6.10 l
EHEIM professionel 3 600
EAN 4011708202364
Article No. 2075020 UPC (-)
For aquariums of about. 240.00 l
For aquariums up to approx. 600.00 l
Pump power (50 Hz) per hour of approx. 1,250.00 l
Pumping head approx. (H max at 50 Hz) 1.80 m
Power(50 Hz) to 16 watt
Filter volume 6.00 l
Pre filter volume 0.50 l
Container volume 9.20 l
As you can see the filter volumes, with nothing inside, are 6.1 and 9.2 litres. With media they become less.
