Soil pH.

gypsum will reduce soil pH.... will also add S and Ca, so that needs to be considered. ph-down what water you add. any simple acid will do, like white distilled vinegar (acetic acid), for one, is readily available and cheap. if it continues to rise, that's very likely microbial causes, unless gaia green has some weird pH relative to the likely ingredients fertilizers are usually acidic, not alkaline. Rhetorical questions.. you'd extrapolate where i'm going... how high is it going? Are there any issues with the plant? if not, as high as 7.2 is "okay", even if it is not optimal.. and if plant is super healthy, i'd not worry so much but would keep eye on it. continue to ph-down whatever you add... if it stays consistent and no probls.. then all good. This wouldn't be obvious unless 5-6+ weeks into grow so that even small isues would be obvious.