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CO2 Reactors vs Diffuser for large aquarium

CO2 Reactor or Diffuser for large 6ft aquarium (for plant growth)

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New Member
7 Jul 2016
Bristol, UK
Hi All, I am new to this forum but I have been directed here for some useful advice.

A little bit of research:
I would like peoples opinions on CO2 reactors and Diffusers (ceramic) and which would be better for a large 6ft aquarium. I have read multiple threads on different forums, some stating that diffusers are better as it provides more "useful" co2 for plants, while others say that reactors are better as it provides near 100% dissolution.

My aquarium setup
6ft 400litre aquarium
1 eheim 2227 wet and dry filter
1 fluval 405 filter
1 eheim 2215 filter
2 sunsun wavemakers
2 300watt heaters
2 58watt jbl 5ft t8 light bulbs
Pressurised co2 (fire extinguisher) with 2 ceramic diffusers (each rated for 300litres)
Denerle nutribasis 6 in 1 soil with lots of capping gravel
Heavy planted tank with Java Fern, lots of Anubias, swords, moss and crypts.

I initially had the CO2 diffusers in my tank to provide co2 for the plants. However my drop checker was constantly dark blue. I tried increasing the co2 but that didn't help. My water test readings showed everything to be in good range, apart from my co2, which was constantly very low. This meant that my tank has started to show the early signs of algae buildup. One of my diffusers broke while cleaning, which lead me to rethink my method of introducing co2 to my aquarium.

CO2 Reactors vs ceramic diffusers
Do you think it is worth experimenting with a reactor? I could still run one of the diffusers in conjunction with the reactor. What are your experiences of using a reactor in a large aquarium with regards to plant growth. Or maybe I am doing something wrong with my pressurised co2? Or maybe my lighting is not enough and I should invest in additional lighting?

For now I am supplementing my tank with EASYCARBO carbon and plant fertiliser (the recommended daily allowance). However even with the easycarbo carbon, my drop checker still shows dark blue and my water test shows very low co2 levels.

So what will your advice be for me? Experiment with a co2 reactor or possibly get better diffusers (I don't mind fine bubbles in my tank). What reactors / diffusers do you recommend? Maybe I need to increase my lights?

Thank you very much for any help given. And sorry for such a long explanation.


11 Oct 2009
Reactors are thin on the ground so trying to find one might prove difficult to start with!
You can quite easily DIY one if you are that way inclined?
2 x in line atomizers would work well but would also require more equipment.
I would be tempted to get another fire extinguisher and set up two UPs, I would consider more light too, maybe another two bulbs.


Global Moderator
25 Jan 2012
However even with the easycarbo carbon, my drop checker still shows dark blue
Easy carbo does not affect drop checkers. Drop checkers work by CO2 gas coming out of the water and crossing the air gap and into the indicator solution. That is why drop checkers are superior to pH pens and other testing methods, as the indicator solution is isolated from the tank water and is not affected by anything in the tank water.

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