CO2 effect one part of a tank?


Junior Poster
Jun 26, 2007
Is it possible for CO2 to only benefit one end of a 6' tank?
On my 125gal I have my CO2 reactor inline on my Eheim 2215 but nothing on the Eheim 2026. The where the CO2 is injected is doing great but the other end of the tank has some Green Spot Algae on the glass and some hair algae on the substrate. Could it be that my whole tank is not receiving the full benefit of the CO2 due to the lower flow rate of the 2215? If so, how would I go about putting a splitter on it to add a reactor to the 2026? Or is there another solution I haven't mentioned? I really would like to be able to employ my inline reactor in some way since I get 100% absorption with it.


Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
Why not have one filter return at one end, with it's inlet at the opposite end? Then reverse that for the other filter. I would expect this to mix the water much better from end to end. The CO2 concentration does vary a lot from one place to another in my tank too. I have my spray bar blowing back to front at one end of the tank, with the inlet at the other end at the back. I figured this would give good circulation, but I'm finding that the CO2 at the front corner across from the inlet is significantly lower than other areas. I can tell this because the fish that don't particularly like having CO2 in the water are more clustered in that corner than any other area, and my drop checker there reads a green-blue-green, where with everything else the same, when the drop checker was at the other end, it read a strong green to yellowish green. I don't see any other effect on the tank, but it does make me wonder just how possible it is to get uniform distribution of CO2 in a tank.

Tom Barr

Staff member
Jan 23, 2005
In answer to your question, yes, and the larger the tank, the more likely you can see the affect.

If you increase the current, add another inlet, another reactor, disc etc, keep plants pruned and tidy, have some decent surface movement etc, then you can resolve the issues.

Tom Barr