Setting: DWC hydro setup, indica, day 45 with ten/fifteen days to go. Leaf tips show slight overfert burn so after the last flush, no more nutes added. Just clean water to the existing nutes until time to flush. OK! Problem: pH starts going wacky dropping from 5.6 to 4.1 overnight. Then lower fan leaves start turning yellow, but not uniform. Still just a little green on the veins. The leaves that receive the most light turn yellow the fastest. No noticeable curling of leaves. Went back to a little bit stronger nute mix for the last few days of flowering (GH series at 2-2-6/gallon w. epsom and protekt). Hypothesis: Mg or N defiency. Question: Should extra be added to the nute mixture or not worry too much because its close to harvest?