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Commencer gratuitementWhat is pH?
pH measures how acidic or alkaline your nutrient solution is. The scale goes from 0 to 14 — 7 is neutral, below is acidic, above is alkaline. In hydroponics, you care about the range between 5 and 7.
What many beginners don't know: pH doesn't affect how many nutrients are in the solution — it affects whether the plant can absorb them at all. You can buy the most expensive fertilizers and still have starving plants.
A difference of 1 pH unit means 10× more acid or base. pH 5 is 10× more acidic than pH 6 — not just a little bit.
Optimal pH for Hydroponics
The golden range is between 5.5 and 6.5. In this window, almost all nutrients are simultaneously available. Outside of it, individual nutrients start to precipitate or lock out — even if they're present in the solution.
As a starting point, we recommend pH 6.0. This is optimal for most plants and gives you buffer on both sides. Small natural fluctuations between 5.8 and 6.2 are perfectly normal and even desirable.
Leafy greens (lettuce, spinach): 6.0–7.0 · Tomatoes, peppers: 5.5–6.5 · Herbs (basil, mint): 5.5–6.5 · Strawberries: 5.5–6.0 · Cannabis: 5.5–6.0
Measuring pH
There are three methods — with very different accuracy:
Test Strips
Cheap, but inaccurate. Only show rough values — too unreliable for hydroponics.
Liquid Test Kit
Better than strips, but still color comparison. Works well as a backup.
Digital pH Meter
The only reliable method for serious growing. Available from ~€15. Calibrate regularly.
A digital pH meter drifts over time. Calibrate it at least once per month using calibration solution pH 4.0 and pH 7.0.
Correcting pH
When pH is outside the optimal range, you need pH-Up or pH-Down solutions. These consist of diluted acids or bases and are available at any grow shop.
pH too high (above 6.5) → pH Down
Add pH-Down drop by drop, stir, wait, measure again. Never add large amounts at once — pH solutions are concentrated and react quickly.
pH too low (below 5.5) → pH Up
Same approach with pH-Up. Potassium hydroxide (KOH) is most common and leaves potassium as a nutrient in the solution.
Plants consume nutrients at different rates, which shifts pH. Measuring daily is ideal, but at minimum every 2-3 days.
Common pH Mistakes
Nutrients change pH. Always add nutrients first, then adjust pH.
An uncalibrated meter lies to you. Monthly calibration is mandatory.
Always correct in small steps. Overshooting leads to a pH yo-yo effect.
Frequently Asked Questions
Daily is ideal, especially in the first weeks. With experience, 2-3 times per week is sufficient. Always measure more frequently with new plants or after nutrient changes.
Yellow leaves can have many causes, but pH problems are one of the most common reasons in hydroponics. Check pH first, then EC. If pH is 5.5–6.5 and EC is normal, the problem lies elsewhere.
Below pH 5.5, calcium and magnesium become hard to absorb. The plant shows deficiencies despite normal feeding: dark spots, leaf curling, slowed growth.
Above pH 7.0, micronutrients like iron, manganese, and zinc precipitate out of the solution. The plant shows chlorosis (yellowing between leaf veins) as the first sign.
Technically yes, but not recommended. Household vinegar contains organic acids that are broken down by bacteria, causing pH to rise again. pH-Down solutions are more stable and reliable.