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Re: measuring CO2



Sharon S.,

The great thing about the internet is the amount of information that is 
available on it. The worst thing about the internet is the amount of 
information that is on it. "Carbonate hardness (KH) is the measure of 
bicarbonate (HCO3-) and carbonate (CO3--) ions in the water." (from my very 
favorite article on water chemistry, at 
http://www.thekrib.com/Plants/CO2/khgh.html. Adding baking soda to your tank 
to adjust the KH does not throw off the KH/pH/CO2 chart, because the KH 
reading changes to reflect the change in the chemistry of your tank. Adding 
phosphate buffers can, although at very low levels (such as using KH2PO4 to 
add P to the tank) the amount it will throw off the chart is less than the 
uncertainty due to how accurate your KH and pH test kits are.

My water here outside of Portland, OR is similar to yours. I add baking soda 
to get it up to around 4-5.5 KH. This will raise the pH (given the same 
amount of CO2) and give you a little more buffer in case of CO2 fluctuation.

-rs



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