Ok, my conundrum continues. I tested both the tank water and freshly made up water today for Mg. It was 1250 ppm for the tank and 1200 for the new water. It was made over 2 days ago so that shouldn't be an issue. Now it seems that every time I do a WC, the Mg level would drop. If it's not one thing, it's another.
Speaking of which, while testing the PO4 today, I got an initial reading of 0.09, which was quite a bit higher than the usual 0.05-0.06 that I've been getting the past few weeks. I had two cuvets stored in RODI so I decided to check again with the second cuvet and it read 0.05. Now that was weird. Test again using the first cuvet and again it read 0.09. Long story short, I bought 4 new cuvets and caps about a month ago. So I got out a third cuvet that I have not used yet and it read 0.05. Is it possible that a simple glass cuvet could be faulty? I swear, sometimes I don't know what to believe anymore :mad2: