When pH is too low
The poster says acidic input below the optimal range can cause nutrient lockout and poor uptake.
Symptoms or effects listed
limited calcium, magnesium, potassium and phosphorus uptake, root stress, slow growth and unstable pH swings
Target pH ranges by medium
Hydroponic systems: 5.5 to 6.0.
Coco coir: 5.8 to 6.2.
Soil or living soil: 6.2 to 6.8.
When pH is too high
The poster says alkaline input can lock out iron, manganese, zinc, copper and phosphorus.
It also lists reduced uptake, pale new growth and slow or stunted growth as outcomes.
Adjustment tips
To lower pH
hydro, coco and soil all show pH down based on phosphoric acid or citric acid, while soil also includes elemental sulfur
To raise pH
hydro uses pH up or baking soda, coco uses pH up or baking soda, and soil uses pH up or dolomite lime
The poster advises adding small amounts, then testing and adjusting rather than making large swings.