The idea is to adjust the water in the drop checker to a KH of 4 so when your pH hits 6.6 the drop checker becomes geen indicating 30 ppm CO2 ( ph of 6.6 with KH of 4 equals 30 ppm CO2 ). I believe Hoppy chose that particular KH because a pH of 6.6 using the AP kit gives a very unmistakable green color making it very easy to determine that you're at 30 ppm of CO2. If the drop checker is a blue color you're CO2 is less than 30. If it's yellow your CO2 is above 30. Hope this helps some. |