It's not so much a measurement of the CO2 in the water, but pH is almost directly affected by the ambient CO2 levels in the air surrounding the tank because dissolved CO2 becomes carbonic acid which lowers the pH. Normal seawater out in the ocean is exposed to a pretty stable 350ppm CO2, but in a house the CO2 levels can be greater than 1000ppm, thus increasing the amount of carbonic acid higher than normal seawater. I actually run a CO2 scrubber attached to the air inlet of my skimmer, basically a filter housing filled with soda lime that absorbs CO2, but it isn't helping much. I wanted to see how bad the air was in my house, and just using the multimeter reading of about 5 volts, I think I'm seeing about 1000ppm in the house. Not really sure where to go from here, I already dose kalkwasser, maybe a house ventilation system. From what I've read, opening windows seems to help. Just not in New England in January! Don't really plan on controlling anything with it, just trying to confirm what's going on in the house.
Pretty good write up here if you're really interested:
http://www.reefkeeping.com/issues/2004-09/rhf/
Pretty good write up here if you're really interested:
http://www.reefkeeping.com/issues/2004-09/rhf/
