Oh, there is a difference between ppm in air and in water. Read the text below the calculator.
http://www.lenntech.com/calculators/...er-million.htm
I'll have to study it to get the math. That was my confusion when I wrote to the manufacturer.
So I can hook this sensor to an arduino (in side a drop checker or breather bag) and have the arduino do the math for water (by weight) and control the solenoid to get the proper co2 concentration.