I added
po4 yesterday to my tank in the form of ph down. Will my co2 reading
now be
void because of that buffer? Surely the plants will consume the
phosphate
pretty quickly, If I do a water change over the weekend and do a co2
measurement will it be more accurate? How do you balance things out
between
buffers and co2?

I thought pH down was diluted Sulfuric Acid, which I think means its not
Phosphate and does not contain Phosphate.