Join Date: Aug 2003
Location: Kelowna, BC, Canada
Actually, IF phosphate is throwing it off, it will make the pH lower, in turn making it seem that you have more CO2 than you really do. Knowing this, just keep the reading below 20-30ppm (30 being the max safe limit), and it will never be higher than that, only lower.
One site said that if without injecting CO2, your level seems to be at more than 5ppm, something like phosphates are buffering the water.