Not sure why, I figured it’s either the solution using the cal to neutralize the acid or it’s something to do with the plants metabolism and what it releases back into the solution. 250 is pretty low unless their seedlings. Maybe at 250ppm there aren’t enough buffers in solution? Before co2 I was vegging around 350, early through mid flower about 450. With co2 I’m at 650 in veg and 800 in flower.