Everything you need to know

Setting the pH value correctly in hydroponics

Which pH value is ideal, why it rises and falls, and how I keep it stable at 5.8 with a few drops.

The pH value is the key to ideal nutrient uptake. Learn how to measure it correctly, adjust it and keep it stable for healthy, strong plants.

🎯My target value

Target 5.8

my value for almost all plants

🧪Optimal range

5.5 to 6.5

For most plants

📈Measuring frequency

every 2 to 3 days

daily after mixing, always EC first, then pH

🧪Calibration

2 weeks

meter interval, at least once a month

Contents

What is the pH value?
Why is it important?
Why the pH value rises and falls
Optimal pH range
Measuring the pH value
Calibrating the meter
Adjusting the pH value
Automatic pH control
Tips for stable pH values
What I use for measuring and lowering
FAQ

🧪Basics

What is the pH value?

The pH value measures how acidic or alkaline a solution is, on a scale from 0 (very acidic) to 14 (very alkaline), with 7 being neutral. In hydroponics the pH shows how well your plants can take up nutrients. An optimal pH is essential for healthy, strong plants and a rich harvest.

Important to know: each step is tenfold. pH 5 is ten times more acidic than pH 6, pH 4 already a hundred times. That’s why a few drops are often enough when adjusting.

pH scale: from acidic to alkaline

Very acidic

pH 0 to 3

Battery acid
Lemon juice

Acidic

pH 4 to 5

Blueberries
Acid rain

5.5

Optimal

pH 5.5 to 6.5

Most plants
Ideal nutrient uptake
Nutrient solution in the tower, my target 5.8

Neutral

pH 7

Pure water
Neutral range
a lot of tap water is at 7 to 8

Alkaline

pH 8 to 10

Soapy water
Baking soda

Very alkaline

pH 11 to 14

Household cleaner
Caustic soda

Visual pH scale

◀ AcidicOptimal 5.5 to 6.5, my target 5.8Alkaline ▶

Hydroponics sweet spot

pH 5.5 to 6.5: In this range most nutrients are optimally available. At 5.8 the plant can reach all nutrients well.

Problem ranges

•pH below 5.5: magnesium, calcium and molybdenum deficiency
•pH above 6.5: iron deficiency possible, plus phosphorus, manganese, zinc, copper and boron get scarce

📈Nutrients

Why is the pH value so important in hydroponics?

🌱 Nutrient availability

The pH controls which nutrients are available to the plants. If the pH is outside the optimal range, deficiencies or toxic effects can occur even if all nutrients are present.

So the pH decides whether the plant can reach the nutrients that are in the solution. In the range around 5.8 they’re all well available. If the value drifts, individual nutrients are blocked even though they’re there.

Too low

Below pH 5.5: Risk of magnesium, calcium and molybdenum deficiency. Plants can no longer take up important nutrients, which leads to yellow leaves and weak growth. Iron and manganese, on the other hand, are taken up too strongly. This happens quickly if too much pH down goes into the water at once.

Too high

Above pH 6.5: Risk of iron deficiency. Leaves turn yellow between the veins, growth slows down considerably. Phosphorus, manganese, zinc, copper and boron also become less available. Pale, yellowish young leaves are typical.

📖Which nutrient gets scarce at which pH is shown in my book (in German) in the chapter “pH und Nährstoffe” with a diagram. Just check the table of contents.›

Not every deficiency means too little nutrient

If you see deficiency signs, check the pH first. Often it’s just blocking uptake, and more nutrient tends to make things worse.

Why the pH value rises and falls

Lowers the pH	Raises the pH
fresh nutrient (mine lowers it noticeably)	the plant uses up the nutrient
pH down or acid	topping up with limy tap water
	air in the water drives out carbonic acid

Tap water is often at pH 7 to 8. Waterworks deliberately keep it above 7 to protect the pipes. Hard water pushes the pH up further, then you need pH down more often.

My own nutrient already lowers the pH when mixing. For me 0.5 ml per litre is enough to lower it by about 0.5, for example from 7.3 to 6.8. The more nutrient, the stronger. Over time the value then slowly rises again. That’s a good sign: when the plant takes up nitrate, it releases alkaline substances into the water. The stronger it grows, the faster the pH rises.

My own nutrient

Frankie’s liquid nutrient

Seedling and leaf nutrient from one bottle, with calcium and magnesium, made for soft water. For all plants from sowing to the growth phase, leafy plants until harvest.

View in the shop ›

⚡Target values

Optimal pH range for hydroponics

🎯 For most plants: pH 5.5 to 6.5

In this range most nutrients are optimally available and the plants can reach their full potential. My target value is 5.8 to 6.0 for almost all plants.

Special cases

Blueberries	pH 4.5 to 5.5
Lavender	pH 6.0 to 7.0
Mint	pH 5.5 to 6.5
Pumpkin	pH 5.5 to 6.5
Peppers, cucumber, melon, parsley	pH 5.5 to 6.0

Important note

pH values for soil and hydroponics aren’t interchangeable, because nutrient availability and buffering are different.

Tip

Start with pH 5.8 as your target value. It’s a good compromise for most plants and allows small fluctuations.

📖The pH and EC values for all plants are in tables in my book (in German) in the chapter “pH und EC für alle Pflanzen”. Just check the table of contents.›

🧪Measuring

How do you measure the pH value in hydroponics?

1. Digital pH meter (recommended)

✅Precise and fast
Ideal for regular measurements
✅Digital display
Easy to read, no interpretation needed
✅Calibrate regularly
With calibration solutions pH 4.01 and pH 7.00

2. Test strips/indicator solutions

•Cheap and easy
Good for a quick, rough overview
•Colour comparison
You read the colour against a scale, only in rough steps
•No calibration needed
But too imprecise for a target of 5.8

How I measure correctly

Remove the cap and dip the meter into the nutrient solution.
Swirl briefly.
Wait until the number stays still.
Rinse the electrode and put the cap back on, the tip should stay moist.

I always measure at the same time of day, in the tower without a permanent meter every 2 to 3 days, daily for the first days after mixing. And always in this order: first EC, then pH. Every nutrient correction shifts the pH.

Measuring tips

🕒Timing

•Always measure at the same time of day
•Wait approx. 1 hour after feeding
•Measure before refilling

🌡️Temperature

•Ideal: nutrient solution 18 to 24 °C
•Temperature affects the pH value
•Create constant conditions

🧪Procedure

•Rinse the electrode well
•Stir the solution
•Let the value stabilise

Hydroponics book by Frank Wagner: step by step to growing vegetables without soil

My book

Step by step into hydroponics

168 pages, simply explained for beginners and with videos on the topics (in German). Exactly how I grow myself: from sowing to harvest.

More about the book ›

Calibrating the meter

Calibrate at least once a month, more often with heavy use, for example every 2 weeks. You need buffer solution pH 7.0 and pH 4.0.

Rinse the electrode and dab it dry.
Bring the buffer solutions to room temperature.
Dip into pH 7.0 and calibrate.
Rinse, dip into pH 4.0 and calibrate.
Finally check in a solution.

Store the electrode moist in storage solution, never dry and not in distilled water.

Free

Which tower suits you?

A few questions about space, location and what you want to harvest, and you get a recommendation.

To the tower advisor ›

🔄Adjusting

Adjusting the pH value and keeping it stable

Step-by-step guide

Measuring

Determine the current pH value after the EC is set

Adjust

Add pH down or pH up

Mix

Stir the nutrient solution well

Wait

Let it stabilise for 10 minutes

Repeat

Until the target value is reached

Lowering pH (too high)

Use pH down:

▸Phosphoric acid (preferred): Also supplies phosphorus
▸Nitric acid: Also supplies nitrogen
▸Sulphuric acid: For very hard water

Caution: Always add drop by drop! Acids are strong and act fast.

Raising pH (too low)

Dose pH up carefully:

▸Potassium hydroxide: Also supplies potassium
▸Potassium carbonate: Milder alternative
▸Sodium hydroxide: Only in emergencies

Caution: Always add drop by drop! Alkalis are strong and act fast.

Important note

Important note: Use pH adjusters developed specifically for hydroponics to avoid side effects. Household products like vinegar, citric acid or baking soda aren’t suitable because they can cause other problems. Vinegar and citric acid break down quickly in the water, the pH then rises again.

Lowering the pH value: my method

I use phosphoric acid from a small dropper bottle with a nozzle. If the value rises above 6, I add 2 to 3 drops and stay at 5.8. With soft water 2 to 3 drops per 10 litres are enough, hard water needs more. Phosphoric acid keeps the pH stable for a long time.

For beginners a ready-made pH down from the shop is safest, because it’s already diluted. You usually only rarely need pH up. If the value has dropped too far, fresh water usually helps.

Working safely with acid

Phosphoric acid is corrosive. Wear gloves and safety glasses, always add the acid to water and never the other way round, and keep the bottle out of reach of children.

Pro tips for stable pH values

✅Use small amounts and be patient
✅The pH often keeps rising after the first adjustment
✅With big deviations, take several small steps
✅Keep the water temperature constant (affects pH)
✅Mix the nutrient solution well before measuring
✅Record your adjustments with the date for better control, so you see where it’s heading

From my shop

Everything for your soil-free start

HydroFlex Tower for indoors and outdoors, seedling box, seedling station, support rings and my own nutrient. After you buy, I’ll help you on WhatsApp.

To the shop ›

⚙️Technology

Automatic pH control

Nutrient controllers for bigger systems

For bigger systems there’s automatic measuring and control technology (“nutrient controllers”) that monitors the pH around the clock and adjusts it automatically when needed. For a tower at home, a pen or a permanent monitor in the reservoir that shows the value constantly is enough.

Benefits:

✅24/7 monitoring
✅Automatic adjustment
✅Constant values
✅Less work

Disadvantages:

⚠️High purchase costs
⚠️Maintenance required
⚠️Technical understanding needed
⚠️Depends on electricity

✅Checklist

Tips for stable pH values

What you should do

✅Quality nutrients: Use hydroponic-specific nutrients for stable pH values
✅Regular checks: Measure every 2 to 3 days, daily after mixing and especially when changing systems
✅Calibration: Calibrate and look after the pH meter regularly
✅Cleanliness: Keep the nutrient solution clean, avoid algae
✅Order: first EC, then pH

What you should avoid

❌Adjusting too fast: Always go step by step
❌Uncalibrated meters: Lead to wrong values
❌Wrong nutrients: Only use products suitable for hydroponics
❌Ignoring temperature: Measure at a constant temperature

What I use for measuring and lowering

Chemdiscount 1Liter (ca. 1,6kg) Phosphorsäure (H3PO4) 85%

Phosphoric acid for lowering. I decant it into a small dropper bottle with nozzle. Corrosive, store safely.

* Affiliate-Link: Bei einem Kauf erhalte ich eine Provision, dein Preis bleibt gleich. Preis inkl. MwSt., zzgl. Versand, Stand 8.11.2026. Bilder: Amazon Creators API

Bluelab OnePen - ein 3-in-1 Temperatur-, EC/PPM- und pH-Messgerät, blitzschnelle Messwerte - Bluetooth-Datenaustausch & In-App-Tracking...

My meter for pH, EC and temperature in one pen, with app.

* Affiliate-Link: Bei einem Kauf erhalte ich eine Provision, dein Preis bleibt gleich. Preis inkl. MwSt., zzgl. Versand, Stand 8.11.2026. Bilder: Amazon Creators API

Measury pH Kalibrierlösung 4.00 + 7.00 - Pufferlösung je 250 ml Eichlösung | Kalibrierflüssigkeit Set Made in Germany, Eichflüssigkeit...

Calibration solution pH 4 and 7 for monthly calibration.

* Affiliate-Link: Bei einem Kauf erhalte ich eine Provision, dein Preis bleibt gleich. Preis inkl. MwSt., zzgl. Versand, Stand 8.11.2026. Bilder: Amazon Creators API

* Affiliate links: I earn a commission if you buy, your price stays the same.

My recommendation for getting started

5-in-1 meter for pH, EC, TDS and temperature

Affordable, easy to use and perfectly adequate for beginners.

View on Amazon* ›

* Affiliate link: I earn a commission if you buy. Your price stays the same.

Conclusion

The pH value is one of the most important factors for successful hydroponics. With regular checks, quality meters and step-by-step adjustments you create ideal conditions for your plants. Invest in a good pH meter and calibrate it regularly: it’s the basis for healthy, productive plants. I keep my value at 5.8 and always set the EC first, then the pH.

FAQ about the pH value

Which pH value is ideal for hydroponics?

For almost all plants the good range is between 5.5 and 6.5. I set my nutrient solution to 5.8. That’s where the plant can reach all nutrients well.

Why does the pH value rise in the nutrient solution?

The plant uses up the nutrient, limy tap water comes in when topping up and air in the water drives out carbonic acid. A slowly rising pH is completely normal.

What’s the best way to lower the pH?

For beginners a ready-made pH down is safest. I use phosphoric acid from a dropper bottle myself, 2 to 3 drops per 10 litres are enough with soft water.

Can I use vinegar or citric acid?

Better not. Both break down quickly in the water, the pH then rises again. Phosphoric acid or ready-made pH down last much longer.

What happens at a pH below 5.5?

Calcium, magnesium and molybdenum get scarce, iron and manganese are taken up too strongly. In that case add fresh water instead of correcting further.

What happens at a pH above 6.5?

Iron and some trace elements become less available. The young leaves turn pale. Lower the value drop by drop back into the range around 5.8.

Should I set the pH or the EC first?

Always the EC first, then the pH. Every addition of nutrient shifts the pH, so the pH comes last.

How often do I need to measure the pH value?

In the tower without a permanent meter every 2 to 3 days, ideally always at the same time of day. After mixing, measure daily for the first days. With a monitor in the reservoir you have the value in view all the time.

How often do I need to calibrate the pH meter?

At least once a month with buffer solution pH 7.0 and pH 4.0, more often with heavy use, for example every 2 weeks.

Do I need pH up?

Only rarely. With soft water and lots of nutrient the value can drop too far. Then fresh water usually helps.

Are test strips enough for measuring pH?

For a rough overview yes. They only show the value in rough steps via a colour comparison. To hit 5.8 exactly, better use a digital pH meter.

Which acid is best for lowering the pH?

Phosphoric acid, because it also supplies phosphorus and keeps the pH stable for a long time. Nitric acid supplies nitrogen, sulphuric acid tends to be used with very hard water.

What do I use to raise the pH?

A pH up based on potassium hydroxide or potassium carbonate, drop by drop. Sodium hydroxide only in emergencies, because sodium stresses the plants.

What is a nutrient controller?

A device that measures pH and EC around the clock and automatically adjusts when needed. It’s mainly worth it for bigger systems, but costs more and needs maintenance.

Do pH values from soil also apply to hydroponics?

No. In soil the ground buffers, in hydroponics it doesn’t. That’s why the good range in hydroponics is lower, at 5.5 to 6.5.

Questions about your setup? Message me on WhatsApp.

Tapping opens WhatsApp (provider: WhatsApp Ireland Ltd.). More in the privacy policy.

Setting the pH value correctly in hydroponics

What is the pH value?

pH scale: from acidic to alkaline

Visual pH scale

Hydroponics sweet spot

Problem ranges

Why is the pH value so important in hydroponics?

🌱 Nutrient availability

Why the pH value rises and falls

Optimal pH range for hydroponics

🎯 For most plants: pH 5.5 to 6.5

Special cases

Important note

Tip

How do you measure the pH value in hydroponics?

1. Digital pH meter (recommended)

2. Test strips/indicator solutions

How I measure correctly

Measuring tips

🕒Timing

🌡️Temperature

🧪Procedure

Calibrating the meter

Adjusting the pH value and keeping it stable

Step-by-step guide

Measuring

Adjust

Mix

Wait

Repeat

Lowering pH (too high)

Raising pH (too low)

Lowering the pH value: my method

Pro tips for stable pH values

Automatic pH control

Nutrient controllers for bigger systems

Benefits:

Disadvantages:

Tips for stable pH values

What you should do

What you should avoid

What I use for measuring and lowering

Further reading

Conclusion

FAQ about the pH value