Good point not sure on the co2, I would doubt very much as alkalinity is about 350ppm carbonate hardness with a ph of about 7.2 (assuming the water is fresh from the well and didn't sit in my algae caked greenhouse water lines overnight). And yes I am measuring with the inlines from spectra-pure. I do have a quality ec meter for use in the greenhouse, it doesn't measure in ppm but the conversion is no problem. I'll have to test with my good specturm meter and see what kind of numbers I get. Overall I'm pretty happy with my consumption of di.