Soil ph trending downward

Here, I’d like to add something – I’ve researched this before: Why does the pH value in the substrate change during cannabis growth and flowering phases? During the vegetative phase, the plant absorbs a lot of nitrogen and releases hydrogen ions (H⁺) into the substrate. This makes the medium more acidic, so the pH drops. In the flowering phase, the plant mainly takes up phosphorus and potassium, which results in fewer H⁺ ions being released. This makes the substrate more alkaline, so the pH rises slightly. These natural shifts are caused by the ion exchange during nutrient uptake.

in addition to all of that.. runoff is not necessarily painting an accurate picture in the substrate... the progress further downward is a concern (rather it be a consistent offset than continueally trending in one direction or the other). add more base to your fertigation/irrigation. don't over do it. ph is log scale. it'snot a straight line. further from 7 the bigger the 'effect' it'll have. 6 vs 7 is much smaller than 5 vs 7 (and equally so in the opposite alkaline direction)

Don't worry about 6.1, just add water at desired Ph and everything should stay in range.

So, give them some ph up and get it back to 6.5. Keep in mind it takes 4x ph up then down. If you haven't you might want flush first then adjust. Maybe give 2 tbls Epsom salt (magnesium) vs calmag.

Guess everything was already mentioned below, got nothing to add. The CalMag will be important for the lady upper right corner. She shows the first deficiency’s. Happy growing 👊🍀🖖

As plants grow, the pH of the surrounding medium tends to become more acidic over time due to the plant's nutrient uptake and other processes. This acidity is related to base saturation. Base saturation refers to the percentage of negatively charged sites on soil colloids occupied by base cations (Ca, Mg, K, Na). These base cations are important for nutrient availability, soil structure, and buffering ability. Ph isn't just a number, At a soil pH of 7, the soil is considered to be 100% base-saturated, meaning that all available sites on the soil colloids (like clay and organic matter) are occupied by exchangeable basic cations (like calcium, magnesium, potassium, and sodium). This also implies that the cation exchange capacity (CEC) is fully occupied by these base cations. Judging by the interveinal chlorosis, your plant is beginning to show on its leaves, probably start with some cal mag, see how she responds. Plants utilize a significant amount of magnesium in certain conditions, especially during periods of high growth, stress, and when certain nutrient balances are disrupted. She could just need a extra dose.