DOC №091SEC: NUTRIENTSREV: 2026-05-15AUTHORED
pH Management in Hydroponics — The Complete Guide
pH controls every nutrient uptake. This guide explains the 5.5–6.5 sweet spot, how to test, how to adjust, and how to stop pH drift.
BY ROOTLESS FARM
Quick answer
Maintain hydroponic reservoir pH between 5.5 and 6.5 (ideal 5.8–6.2). Test with a calibrated pH pen daily; adjust with food-grade phosphoric acid (pH down) or potassium hydroxide (pH up). Drift more than 0.3 in 24 hours signals an old solution — replace it.
Use the calculator
// RESULT — ADD
40.0 mL pH Down
Estimate based on typical food-grade phosphoric/potassium hydroxide. Add half, wait 10 min, retest, top up.
Why pH drifts
- Plants take up cations and anions at different rates.
- Algae or biofilm raises pH as photosynthesis consumes CO₂.
- Old solution accumulates plant exudates that buffer in unpredictable directions.
Fixes
Replace 50% of reservoir weekly. Cover the reservoir to block light. Calibrate the meter monthly with 4.01 and 7.00 buffers.
FAQ
2 entries- Q01Why is hydroponic pH so important?
- Outside 5.5–6.5, individual nutrients become chemically unavailable even when present. Iron locks out above 6.5; calcium and magnesium below 5.5.
- Q02How often should I check pH?
- Daily for the first month, every 2–3 days once a routine is established.