The pH range recommended for most greenhouse crops is indicated by slashed lines. This is due to the substrate components typically used in nursery and greenhouse production. The recommended range of irrigation water pH and substrate solution pH for production depends on the crop being grown. In general, pH should range from 5.2 to 6.8 for irrigation water and 5.4 to 6.3 for substrate solution. If the pH and alkalinity are high, your water may need acid treatment prior to use on crops.
Alkalinity is a measure of a water's capacity to neutralize acids.
Ammonia, borates, organic bases, phosphates, and silicates can also be minor contributors to alkalinity. In most cases, this is a safe assumption. Even though Grower B's water is one pH unit lower than Grower A's, it takes more than four times more acid to lower the pH to 5.8 due to the differences in alkalinity. Both alkalinity and pH are must be considered when adjusting the pH of water. Titrations of two different waters with sulfuric acid.