Hydroponic pH and EC: Reading the Numbers on Your Tester

Your system is running, the seedlings look fine, and the tester shows two numbers that mean nothing yet. Hydroponic pH and EC are those numbers, and reading them takes two minutes once you know what normal looks like.

Quick answer: For hydroponic pH and EC, hold the nutrient solution between pH 5.5 and 6.5. Match EC to the crop: about 1.2 to 1.8 mS/cm for lettuce, 2.0 to 4.0 for tomatoes. Check both twice a week, same time of day. Then calibrate the tester monthly.

Key takeaways:

• pH shows how acidic the water is. EC shows how strong the nutrient mix is.
• Australian tap water reads pH 6.5 to 8.5. So a high number before nutrients is normal.
• A cheap pen drifts. Calibrate with pH 4 and pH 7 buffers and a 1.41 mS/cm standard.
• Instead of chasing the second decimal, watch the pH and EC trend across the week.

This guide is for: Beginners

What does your hydroponic pH and EC tester actually measure?

A hydroponic pH and EC tester measures two separate things in the same cup of water. pH is how acidic or alkaline the water is, on a scale of 0 to 14, where 7 is neutral. EC is electrical conductivity, a count of the dissolved mineral salt. That means EC stands in for nutrient strength.

The names are less scary than they look. pH is short for potential of hydrogen: the more free hydrogen ions in the water, the more acidic it reads, and each full step on the 0 to 14 scale is a tenfold change. EC works because nutrients are mineral salts. Dissolved salts split into charged ions, and ions conduct electricity. So the more nutrient in the tank, the more current the water carries - that is the conductivity the meter reads (Oklahoma State University Extension, 2017).

So your hydroponic pH and EC readings answer two questions. pH answers whether the plant can take the food up. Then EC answers how much food is in the tank. A solution can sit at a perfect EC and still starve the plant, because the wrong hydroponic pH level locks nutrients away.

Most home meters show EC in mS/cm, short for millisiemens per centimetre. Also, some show ppm, a converted figure rather than a second measurement. In practice, mS/cm is the unit used across the hydroponics for beginners guides.

What should the numbers say? Target ranges by crop

Most crops sit between pH 5.5 and 6.5 in the tank. In practice, soilless solutions are held at pH 5 to 6, so the root zone settles between 6 and 6.5, where nutrients stay most available (Oklahoma State University Extension, 2017).

Crop	EC (mS/cm)	pH
Asparagus	1.4 to 1.8	6.0 to 6.8
Basil	1.0 to 1.6	5.5 to 6.0
Bean	2.0 to 4.0	6
Bok choy (pak choi)	1.5 to 2.0	7
Broccoli	2.8 to 3.5	6.0 to 6.8
Cabbage	2.5 to 3.0	6.5 to 7.0
Capsicum	0.8 to 1.8	5.5 to 6.0
Celery	1.8 to 2.4	6.5
Cucumber	1.7 to 2.0	5.0 to 5.5
Eggplant	2.5 to 3.5	6
Leek	1.4 to 1.8	6.5 to 7.0
Lettuce	1.2 to 1.8	6.0 to 7.0
Okra	2.0 to 2.4	6.5
Parsley	1.8 to 2.2	6.0 to 6.5
Rhubarb	1.6 to 2.0	5.5 to 6.0
Spinach	1.8 to 2.3	6.0 to 7.0
Strawberry	1.8 to 2.2	6
Tomato	2.0 to 4.0	6.0 to 6.5
Zucchini (courgette)	1.8 to 2.4	6

Source: Oklahoma State University Extension, 2017.

So treat that as a hydroponic pH chart, not a set of hard limits. Lettuce does not die at pH 6.8, and a tomato at EC 1.9 is not starving. But a plant left outside its band for a week shows it: pale leaves, slow growth, or tips that burn when EC runs high. For anything else, the full crop list covers what grows indoors here.

Growth stage nudges those numbers too. So seedlings want a gentler mix, about half-strength nutrient at the bottom of the crop's EC band. In practice, leafy growth sits mid-band. Then fruiting crops, like a tomato setting trusses, run at the top of their band. The pH targets stay the same the whole way through.

How I check pH and EC on the Sunshine Coast

My own testing happens in a kitchen at Sippy Downs, on the Sunshine Coast, and the routine is dull. So I test twice a week, always before I top the tank up, because topping up first hides what the plants have done.

Every product in the range was tested at home before it was added to the catalogue, so these habits come from running the machines, not a spec sheet. For example, lettuce took 25 to 35 days from seed to a cut head in that setup.

So the number I care about is not the second decimal. It is the direction of travel between Monday and Thursday. That is the same habit as the germination guide: check, note, adjust once.

What will your tester read on Australian tap water?

Straight tap water in Australia usually reads between pH 6.5 and 8.5 before any nutrient goes in. The Australian Drinking Water Guidelines state that "the pH of drinking water should be between 6.5 and 8.5" (NHMRC). In practice, that band protects pipes and fittings, rather than plants.

So a tap reading of 7.6 is not a fault. It is the starting point. Then, once nutrient concentrate goes in, the mix pulls the number into the growing range.

What is tap water pH doing later in the week, though? That comes down to alkalinity, the water's buffering strength. For example, alkalinity above 75 ppm pushes solution pH back up over the following days (Oklahoma State University Extension, 2017). From the Sunshine Coast to Brisbane, that slow climb is why a beginner's reading drifts.

Is your tester telling the truth? Calibration and care

An EC meter for hydroponics does not have to be expensive. But it does have to be calibrated, because a drifted pen lies with confidence.

For pH, use pH 7 and pH 4 buffers, rinsing the probe between them. Then for EC, use a 1.41 mS/cm standard, the reference the Oklahoma State University Extension guide uses.

How to calibrate a pH meter comes down to three habits. Do it monthly, at room temperature, because a cold probe reads differently. And store the probe wet, never dry: a dried-out bulb kills a cheap pen.

Which pH meter or tester do you actually need?

A digital pen that reads pH, or a combined pH and EC meter, is the practical choice for a home system. One probe, both numbers, and calibration keeps it honest. Paper test strips are the cheap backup: fine for a rough check, hard to read against a coloured nutrient mix, and silent on EC.

Liquid hydroponic pH test kits sit in between - accurate enough, but slow once testing becomes routine. So for a benchtop system, a combined hydroponic pH meter that also reads EC covers the whole weekly routine with one tool.

Also, our 4-in-1 water quality tester reads pH, TDS, EC and temperature from one probe.

What are ppm and which scale is your meter using?

Ppm means parts per million, and it is not a separate measurement. It is EC converted with a scale factor, and your manual states which one. So what are ppm in water on one meter can read differently on another.

For example, an EC of 1.4 mS/cm shows as 700 ppm on a 500-factor meter, and 980 ppm on a 700-factor one. Same water, two numbers 280 apart. That is arithmetic, not a change in the tank. So read an EC meter in mS/cm and treat ppm as a translation.

pH too high or EC too low: what should you do?

Read the direction before you reach for a bottle. pH that climbs over three or four days points to alkalinity in the tap water. EC that rises on its own means water is evaporating faster than the plants feed. So top up with plain water. EC that falls means the plants are eating. Then add concentrate at half the dose you expect. If you are not sure what that concentrate actually contains, our guide to hydroponic nutrient solution breaks down the A and B bottles.

A green tank muddies all of this, so clear the film before you trust a drifting reading. Our guide to algae in a hydroponic system explains what it does to your numbers.

Order matters when you fix both. Set the strength first, then the acidity - the Oklahoma State University Extension guide is blunt about it: "pH should always be checked after getting the EC into the optimum range." Dosing pH first just gets undone by the nutrient top-up that follows.

How do you lower hydroponic pH in practice? pH Up and Down are the two bottles you need, and Down does most of the work. Inside the bottles there is no mystery: Down is usually phosphoric or citric acid, Up is potassium hydroxide or carbonate (Oklahoma State University Extension, 2017). Add a small amount, stir, wait fifteen minutes, then re-test. The mistake to avoid is chasing decimals, which turns into dosing, testing too soon, then swinging back. A reading that wanders inside the band is not a problem to fix. It is normal movement.

Also, a dosed self-watering system holds its range better than an open bucket, so the tester becomes a weekly check. It still drifts, just slower. For a pump-cycled tank, the automated NFT system keeps water moving through the channels.

The 2-minute weekly pH and EC routine

Hydroponic pH testing is a habit, not a science project. Here is the whole routine. Test pH and EC at the same time of day, twice a week, before any top-up. Then write both numbers in a phone note with the date. Top up with plain water if EC has risen, or add nutrient if it has dropped. Adjust pH only outside 5.5 to 6.5. An open bucket or tub is worth a daily glance. But a dosed machine holds steady with the twice-weekly check.

Then run a full hydroponic water change every two weeks. The Oklahoma State University Extension guide advises a full replacement on that cycle, and a fresh mix resets both numbers. Keep the solution near 22 to 24 C while you are at it - the same guide lists that water temperature as optimal, and a cold tank reads differently. In practice, that one habit fixes more beginner problems than any amount of dosing. Treat both as starting points, not rules. So a heavily planted tank may need a fresh mix sooner, and in a warm room the cooler end of that band holds more oxygen in the water.

FAQ

What is tap water pH?

Tap water in Australia sits between pH 6.5 and 8.5. The Australian Drinking Water Guidelines set that band for the supply, so 7 to 8 from the tap is expected. Then nutrient concentrate pulls it toward the growing range.

How much pH down to use per litre?

There is no safe fixed dose per litre: products differ in strength, water differs in alkalinity. Instead, add a very small amount, stir, wait fifteen minutes, then re-test. Note how far that moved your reading, then reuse the figure.

How do you calibrate an EC meter?

Rinse the probe, then sit it in a 1.41 mS/cm calibration solution at room temperature. Press the calibration control and wait for the reading to settle. Then rinse again and check the manual for storage.

How do you test pH and EC at home?

Rinse the probe in clean water, switch it on, and dip it into the tank away from the pump. Wait until the number stops moving, note the reading, then rinse again and store the pH probe wet. On a combined meter you test EC the same way, with the same probe.

How do you lower hydroponic pH?

Use pH Down in small amounts while the water is moving. Wait fifteen minutes before re-testing. However, if the reading climbs back within a day, alkalinity is the cause, not the dose (Oklahoma State University Extension, 2017).

How do you raise hydroponic pH?

Use pH Up - usually potassium hydroxide or carbonate - in small doses while the water is moving. Then wait fifteen minutes and re-test (Oklahoma State University Extension, 2017). A reading that sits only slightly low is rarely worth chasing. But if it keeps drifting low, mix a fresh solution and restart from the target band.

Why is pH important in a hydroponic system?

pH decides whether the plant can absorb what is already dissolved in the water. But outside roughly 5.5 to 6.5, some nutrients bind up and stay in the tank, so a well-fed solution still leaves pale plants. That is why pH is checked alongside EC.

Do you need a pH controller or dosing system?

Not for a benchtop system. An automatic pH controller or doser earns its keep once you run several large reservoirs, where drift compounds quickly. But at home scale, a twice-weekly manual check holds the band, and a dosed machine narrows drift on its own. So spend on a reliable meter before any automation.

About the writer

Laszlo Bulatko founded LaNiTex Hydro Garden in December 2024 and runs it from the Sunshine Coast, Queensland (Sippy Downs). He tested each system at home before it was listed, a one-off check per product. Before hydroponics he spent 15 years in sales, marketing and brand development in the Hungarian fishing-tackle trade, after starting out at IBM and Diageo. He now places grow boxes in Queensland primary school classrooms through Term-Grow Enrolment. LaNiTex Australia Pty Ltd, ABN 47 682 768 967. Got a reading this guide does not explain? Send it through. More: about Laszlo Bulatko.

Sources

The hydroponic pH and EC figures here come from two published sources, both checked on 22 August 2026.

• NHMRC, Australian Drinking Water Guidelines, pH fact sheet. https://guidelines.nhmrc.gov.au/australian-drinking-water-guidelines/part-5/physical-chemical-characteristics/ph
• Oklahoma State University Extension (2017), "Electrical Conductivity and pH Guide for Hydroponics", HLA-6722. https://extension.okstate.edu/fact-sheets/electrical-conductivity-and-ph-guide-for-hydroponics