Fertigation Acid & Dose for Target pH

Most irrigation water is alkaline, which precipitates calcium and magnesium and lets phosphates and micronutrients lock up — clogging emitters and lowering nutrient availability. Injecting acid lowers the water pH to roughly 5.5–6.5, keeping those nutrients soluble, preventing scale and biofilm, and keeping drip lines and drippers flowing freely.

The dose scales with the water volume, the size of the pH drop you want and the strength of your acid. The calculator estimates the millilitres of acid to inject for the target pH drop and converts it to litres for the whole batch. Because real water buffers differently, the result is a starting dose you then fine-tune with a meter.

For most fertigation a target of about 5.5–6.5 keeps phosphates and micronutrients available and protects the lines without going so low that it harms roots or equipment. Some growers dip lower briefly for a line-cleaning flush. Match the target to your crop, water and the nutrients you are injecting.

Common choices are phosphoric acid (which also supplies phosphorus), sulfuric acid (strong and cheap) and nitric acid (which also supplies nitrogen). Each has a different strength and safety profile, so set the acid-strength input to match your product. Choose based on cost, the nutrients you want to add, and what is safe to handle on your operation.

Alkalinity — the carbonates and bicarbonates in the water — is the buffer that resists pH change, so two waters at the same pH can need very different acid doses. High-alkalinity water needs much more acid to shift its pH. Where you have an alkalinity figure, use it to refine the dose; otherwise treat the result as a buffered estimate.

Inject acid with a calibrated dosing pump into the irrigation stream, never the other way around, and always add acid to water — not water to acid. Wear eye and skin protection, run the system, then measure the pH at an emitter and adjust the rate until it holds at target. Re-check whenever the water source or fertiliser changes.

A periodic acid flush at a lower pH can dissolve carbonate scale that has already built up in lines and emitters, restoring flow. Routine acidification to target pH then keeps new scale from forming. Combine with filtration and, where biofilm or algae are the problem, a separate chlorination treatment.

Generally yes, and lower pH keeps many fertiliser nutrients more soluble — but avoid mixing concentrated acid directly with calcium- or sulphate-containing stock solutions, which can precipitate. Inject acid and incompatible fertilisers through separate lines or stagger them, and jar-test a mix before running it through the system.

They are a sound starting dose. The true acid needed depends on your water's alkalinity and temperature and the exact acid concentration, so always confirm with a pH meter at the emitter and adjust. Treat the calculator as a way to get close fast, then dial it in and re-check as conditions change.