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CO2 and O2 - a clarification
I realize my earlier posts on gasses dissolved in tank water were not all
that clear, and if some people got confused I can see why! Let me try to
summarize in a way that is relevant for the aquarist.
1. Dissolving more of one gas in water decreases the amounts of other gas
(or gasses) that are dissolved. This was the one point I was trying to get
across in my original post; it is a long established principle and really
does not warrant debate.
2. In an aquarium, the amounts of CO2 that are injected will have at worst a
very minor effect on the O2 level. George Booth did the calculations and the
worst case scenario seems to be a 3% decrease in O2 if CO2 is injected to
optimal levels. This decrease in O2 is insignificant and would not cause the
fish any distress.
3. In a planted tank things get complicated. Increasing CO2 causes the
plants to produce more O2, and this extra O2 will probably more than
compensate for the O2 lost due to #2. The end result will be a tank that
contains more O2 and more CO2 in solution and, in accordance with #1, less
Peter G. Aitken