Inline Co2 loop effects on flow?


Mar 7, 2008
I've seen discussion of a Co2 setup where a loop with an inline, fractionating powerhead is placed on the canister filter outflow. I'd like to give this a try but was just wondering whether this impedes flow from the filter at all?

I have an Eheim Ecco on the tank which supposedly puts out 145 GPH and I'd probably go with a MJ 1200, which is rated @ 295 GPH. Any thoughts on how flow would be affected?


Guru Class Expert
Oct 26, 2007
Brisbane, Australia
Cavitation was the first thing that sprung to my mind too.

If the output from the filter is less than what is required for the input of the powerhead, cavitation would occur within the impellor chamber of the powerhead.

In any case, I can't see any way that you could connect any 2 pumping devices together to obtain any benefit? Something is going to be 'the weaker link', which is going to bottleneck better flow and possibly damage (cavitation etc) the stronger link.

I suppose you could turn the canister filter off and suck the water through the media contained within it with an external pump, but then hose sizes (i.e. plumbing) may become an issue then too...

I don't think you could do something like this based on rated values anyway. All sorts of factors are going to affect the actual outputs of the pumps.

What exactly is this trying to acheive? Why bother with the CO2 loop of the canister?


I have modified my setup to loop back to the pump in the sump and after tweaking it, it is running very nicely and I get no co2 bubbles in the tank. Here was my original setup:

mag 1200 in sump ===>25micron ocean clear canister==> ext5000 co2 reactor==> tank return

mag (has a T in the intake) ==>canister==>T==>tank return