Co2 DropChecker inconsistent with PH test
I have been in the hobby for a year and a half growing a heavily planted, 20g. So I have been using the same test kits (The solutions one not the bands) and the same Co2 drop checker for the whole period. Obviously changing the drop checker solutions every now and then. Although it is the same bottle as I have bought a year or so ago. For a while my drop checker was consistent with my ph solution test.
My problem is, for 2-3 weeks now, my drop checker has been showing dark green colour which is not good as you know for Co2 levels and when I do a solution test I get a lime green which is what I am aiming for. Exact same products as it use to be. Most of my plants seems to be doing good except some newly added reineckiis who are having a hard time, could not say if it's my lighting schedule or the Co2 which leads me to confusion in knowing if I am lacking Co2 or not.
Since I am still a newbie I am wondering if it possible to get different readings between Ph test and dropchecker that would be both accurate so to speak, if so which one to follow? If not I assume that something is wrong with one of them.
Thank You for your help!!