Co2 Injection Vs Ph Drop

FxFocus

New Member
Aug 17, 2018
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In the context of PH8 GH9 KH5 before adding CO2...
Under what circumstances would you not get a PH drop when injecting CO2?

I ask this after having been told the following...

"You can add CO2 to the point of saturation. After that it's just carbonic acid.
If you stop before the carbonic acid starts to form, no PH drop."

Is this right?
Sounds daft to me but I'm no chemist lol
 

tiger15

Member
Aug 12, 2017
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When you inject CO2, it can enter water in ionic form (carbonic acid) and free form (free gas and mist). A high efficient reactor will turn CO2 into largely carbonic acid. A diffuser will turn CO2 into mist and carbonic acid, and the proportion depends on the type of diffuser. Mist are nano bubbles that you can see. Free gas can be microscopic in size that you can't see, which is in equilibrium balance with carbonic acid according to pH, kH and temperature solubility law.

If you measure pH with pH pen, it measures H+ ions so it detects only carbonic acid. If you measure pH with a liquid indicator, it's a chemical reaction that measures both carbonic acid and free gas because you cap and shake the water sample in a test tube. So if you have lot of CO2 mist, liquid indicator will show lower pH than pH pen.