OKOK. Fed 2 litres solution at pH 6.9. Run off was 7.3. Presume this means soil pH is rising. Still got a few weeks before flush so will lower pH of nutrient solution a bit.
Tdog Howdy;....
I take it, the two on the right of pic no4 above are DP's Durban Poison" Auto's yes ?? they look heavy weight man, your earlier flushes have payed dividend.
TDog;
If it is tap water you are using. And if it is of a high TDS or in other words high in calcium and other alkaline salts. The plant drinks the water and "Leaves" a lot of the un needed calcium carbonates in the soil, as a residue of hard tap water.
This alkaline salt, then builds up in the soil, over weeks of giving salty tap water to the plant. particularly post wk7-8 if no mid grow flush has been given to lower salts, and un-used nute salts as well.
And as it builds up "calcium Carbonates" and others, the "PH, Potenz of Hydrogen" go up or swings in favor of alkalinity, pushing up Ph of the soil by "Cumulative Accumulation", in the substrate.
Hence, flush at 6.9 and 7.3 washes out. To get the soil Ph down, you need to flush with a stronger ion base, "Acid Base", at 5.6, with "Nitric Acid". Flush with 5.6, then you should get, a run off below the critical ceiling of Ph 7.
You need to keep in these uptake ranges relative to soil Ph. Soil temp not below 20c minimum lights out.
Hope is of some help, next run, mid grow flush is a good idea. I flush every 8 feeds, of medium EC feeds. And still a end of veg flush, and a mid flower, as well as the final 10 day harvest flush. That keeps thing on track in the soil. I check run off "Ec" to see how much they are eating as well !!
Automaster.
Ps; my outdoor plants love the high Ec flush water...... they go mental for it !! proof of "Overfeeding"...again !!