If your ph is dead on when ya ph and your letting 20% runoff, then the ph will be fine... I remember a long time ago people suggested to check runoff, am not sure why I did, I know better...so needless to say was fixing issues that were not there... It won't take long get that back under control, 3-4gals through her if in coco ph to 6.0.. then give nutes on 4th or 5th depending how many gals you run through, I tend flush over a few hours, I don't run 4-5 gals right through..