Kratky pH: Testing and Adjusting Your Solution
pH decides whether a plant can actually use the nutrients in its solution. Getting Kratky pH right at the start is one of the simplest ways to avoid yellow leaves and slow growth later.
What pH means
pH is a scale from 0 to 14 that measures how acidic or alkaline a liquid is. 7 is neutral. Lower numbers are more acidic, higher numbers more alkaline. Each whole number is a tenfold change, so a solution at pH 5 is ten times more acidic than one at pH 6.
Why pH matters in hydroponics
A nutrient can be present in the water and still be hard for the plant to absorb if the pH is wrong. Iron and manganese, for example, become less available as pH rises, while other nutrients become less available when it drops too low. In soil, the soil itself buffers pH swings. In hydroponics there is no soil, so the solution's pH has a direct effect on the roots.
The range most Kratky crops like
Most leafy greens and herbs grown hydroponically do well in a slightly acidic solution, commonly given as about 5.5 to 6.5. Many growers aim for the middle of that range, around 5.8 to 6.2, which gives a little room for drift in either direction. Individual crops have their own preferences, so check guidance for the plant you are growing, and your nutrient label, which may recommend a range.
| Reading | What it means | What to do |
|---|---|---|
| Below 5.5 | Too acidic for most crops | Add pH up a drop at a time |
| 5.5 to 5.8 | In range, low side | Leave it |
| 5.8 to 6.2 | The middle of the range | Leave it; ideal start |
| 6.2 to 6.5 | In range, high side | Leave it |
| Above 6.5 | Too alkaline; iron can lock out | Add pH down a drop at a time |
How to test pH
- Test strips. Cheap and simple. Dip, wait and compare the color to the chart. Fine for occasional checks, though colors can be hard to read precisely.
- Liquid drops. Add a few drops to a small sample of solution and compare the color. Similar accuracy to strips.
- Digital pH pen. Gives a number on a screen. Faster and easier to read, but needs calibrating with buffer solution from time to time, and the probe must be kept moist and clean.
Whichever you use, test a sample after the nutrient is fully mixed, because adding nutrient usually changes pH.
How to adjust pH
- Mix the nutrient solution fully first.
- Test the pH.
- If it is too high, add pH down; if too low, add pH up. Use products made for hydroponics.
- Add only a few drops at a time, stir well, and wait a minute before testing again.
- Repeat until the reading is in range.
It is easy to overshoot, especially in a small jar where a single drop makes a big change. Going slowly saves bouncing back and forth between pH up and pH down. Adjusting in a separate mixing jug, before you pour the solution into the reservoir, is easier than adjusting inside a planted kit. The Kratky kit setup guide puts this step in order.
Should you check pH after planting?
In a Kratky system, pH often drifts as the plant feeds. A check once a week or so is useful for learning how your setup behaves, but small drift is normal and not a reason to keep adjusting. Constant adjustment can do more harm than good. If pH moves far out of range and the plants show symptoms, a correction may help. You can test a sample through the water level indicator or by lifting a net pot briefly, taking care not to tear the roots.
Water and pH
Tap water varies widely. Hard water can push pH up and resist adjustment. Softened water is not recommended for plants because of the sodium it can contain. If your tap water makes pH hard to manage, filtered or rain water (collected cleanly) can be an option. Testing your water before adding nutrient tells you where you are starting from.
Symptoms that can point to pH
- Yellowing between the veins of new leaves, often linked to iron becoming unavailable at high pH.
- General poor growth even though the nutrient was mixed correctly.
- Symptoms that look like a nutrient shortage but do not improve with more nutrient.
Many problems look alike, so check pH before changing anything else. The Kratky problems and fixes guide lists other causes to rule out.
Frequently asked questions
Why does my Kratky pH keep rising?
pH often drifts upward as plants take up nutrients, and hard tap water can push it higher. Small drift is normal; only correct it if it moves well outside the range.
Do I need to adjust pH if I use distilled water?
Usually yes. Distilled water has little buffering, so the nutrient sets the pH. Test after mixing and adjust in small steps.
What pH should Kratky lettuce be?
Lettuce is commonly grown at about 5.5 to 6.5, with many growers aiming near 6.0. Check your nutrient label for its recommendation.
Can I use vinegar or lemon juice to lower pH?
Products made for hydroponics are more predictable. Household acids can work in a pinch but are weaker and less stable, which makes small jars harder to adjust accurately.
Key points
- pH controls how easily roots can take up each nutrient.
- Most Kratky leafy greens and herbs like about 5.5 to 6.5.
- Test after mixing nutrient, then adjust a few drops at a time.
- Small drift after planting is normal; do not chase every change.
pH and nutrients work together: read the Kratky nutrients guide alongside this one.