CO2 fertilization

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CO2 fertilization

Postby prussell » Thu Jun 13, 2013 7:43 pm

I do not have a planted tank so I have no experience with CO2 fertilization but I am puzzled by the CO2 diffusers I have seen offered for sale. I presume that their purpose is to delay the rise of the bubble giving longer for the CO2 to be absorbed by the water. However, I wondered my they are considered necessary. Nobody fills the aquarium to overflowing so there is always airspace above the water. Given that CO2 is considerably heavier than air, I reasoned that any CO2 rising to the surface will lie above the water where there is a large surface area for absorption to occur or am I missing something?
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Re: CO2 fertilization

Postby Carylnz » Thu Jun 13, 2013 10:22 pm

Diffusers create more surface area for the bubbles so its more efficient for the water to exchange the gas (more smaller bubbles have more surface area than one big bubble). The small bubbles also rise more slowly providing even more contact time. Inline reactors allow almost complete absorption of CO2 gas so there aren't actually any visible bubbles. The air space above the tank is not efficient at keeping CO2 there (due to the lights and heating and turbulence etc.) and the area of the water surface above the tank is very small compared to the millions of tiny bubbles from a diffuser.
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Re: CO2 fertilization

Postby prussell » Sat Jun 15, 2013 9:36 pm

Thanks Carylnz, that is very useful. On refection, I realise that it could also be detrimental to have a layer of CO2 blanketing the aquarium surface as it might impede the absorption of oxygen.
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