CO2 system & Airstones - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 4 Old 01-16-2011, 10:14 AM Thread Starter
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CO2 system & Airstones

I've heard that running a co2 system and an airstone together defeats the purpose of the co2 system. Is that correct?
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post #2 of 4 Old 01-16-2011, 10:49 AM
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From my understanding the issue comes from the O2 from the airstone breaking the surface tension of the water and allowing the CO2 to escape into the atmosphere. I have heard that getting an airstone, or some form of bubbler that releases very small bubbles will reduce the amount of CO2 lost.

I however do not use CO2 in my tank, so best to let someone else chime in as well.

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post #3 of 4 Old 01-16-2011, 01:53 PM
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The purpose in adding CO2 is to get more carbon dioxide into the water, presumably to increase plant growth or sometimes to lower the pH (it does this notwithstanding). Any device that causes surface disturbance or excessive water movement increases the exchange of gasses at the surface, by expelling CO2 faster and bringing oxygen in faster. So in this regard, the two systems are working at cross purposes.

Assuming your use of CO2 is for plant growth, this can only help during the daylight since plants do not photosynthesize during darkness. Therefore, CO2 diffusion is usually turned off during darkness, otherwise it is just wasted and may cause a serious depletion of oxygen. At the same time, those with heavily planted tanks sometimes suggest running an airstone at night to ensure sufficient oxygen. This is only necessary in tanks with CO2 diffusion during the day.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #4 of 4 Old 01-16-2011, 01:56 PM
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If you use CO2 (at moderate levels), most of the time there's no need for an airstone at night. Your fish will let you know.

I don't use CO2, but this is what my friends have said when I asked them.

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