The crushed coral will affect the pH/KH of the water (the reason it is used), but that will not affect the CO2 reading itself, As the KH of the water must be measured, so that the CO2 computation itself will not be adversely affected - it will be accurate. The concentration of CO2 is not affected by the source of the carbonates/bicarbonates, only by their level in the water at the time of reading.
Aging or aeration a tank water sample will give better data, but is not instant-reading. It does compensate for the non-volitle organics (which do affect the pH) in the water, as their concentration should not shift with aging.or aeration.
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Where's the fish? - Neptune
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