Using A Co2 Reactor In A Sump


Junior Poster
Oct 5, 2013
Has anyone had success with using a stand-alone CO2 reactor in a sump? (versus returning the water to the tank directly)

I'm running a 40 gal sump beneath a 130 gal display tank, and I'm diffusing CO2 directly into the display tank using an Atomic ceramic diffuser. For purely aesthetic reasons, I'd like to remove the diffuser from the display tank. However, I have a large variable speed return pump that is hard-plumbed between the sump and the tank that I'd just as soon leave alone - so I'm not thrilled about the idea of inserting either an inline diffuser or CO2 reactor between the return pump and the tank.

Instead, I'd like to be able to install a stand-alone CO2 reactor in the sump. My idea is to use a dedicated pump to drive flow through the reactor and return the outflow back to the sump. My assumption is that if the CO2 is 100% dissolved in the reactor, and the reactor return is arranged in the same compartment in the sump as the return to the display tank, then I should be able to get CO2-laden water back to the display with little off-gassing.

I know there will be "some" off-gassing as the water passes through the pump and back into the display, but I'm assuming that this would still be more efficient than the in-tank diffuser I'm using now (I see lots of micro-bubbles in the display that make their way to the surface).

Am I thinking about this the right way?

I'm sure someone has tried this before ... can anyone share their experience?


Apr 28, 2015

I run a cerges reactor with its own dedicated pump. I got the best results by feeding the CO2 enriched water from the reactor outlet (via a hose) into the inlet of the return pump. I managed to do this without reducing the throughput of the pump when the reactor pump is off.

My return pump is a Sicce Syncra 5. It has 3 inlets, so I put an elbow at the end of the outlet hose and hook it into one of the outlets. I still need to figure a better way to secure it because it dislodges sometimes, but that's basically it.


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Sep 16, 2015
Hillsboro, OR
The Reactor pump vs return pump speeds is one aspect to keep in mind. If your return pump is not faster than reactor pump, what you will end up is in a situation where you are trying to add CO2 to already enriched water. Water has limited capacity to hold gas so after a while you won’t be able to dissolve any more CO2 if all you water in the final chamber is already fully enriched.
If you return pump is faster, you then have more non enriched/degassed water available.
Now if you try to balance that, you may end up in a place where the reactor pump might not be as strong to dissolve the required CO2.

So things to play with. Bigger sumps turning more water are better for such setups.