ph decrease

Hey all, I would like to ask your support here. I have a 100 gal system for 50 days. Cycling complete: Nh4 0 Nh3 0.001 Nitrite 0 Nitrate 8 ppm Phosphate 0.07 ppm Ph was 8.27 about one week ago with a co2 scrubber. But after following very closely the indicators above I tested the following...