How HWGrow Tests Nutrients: pH, EC and PPM Protocol

Last updated: November 2, 2026

Quick answer: For every product, I mix 1 mL of liquid nutrient or 1 g of dry product into 500 mL of reverse-osmosis water, then record the water’s pH and conductivity-based PPM before and after. It shows me how a product moves a water sample. It is not a feeding schedule.

Video chapters: my test protocol

1. 0:00 — Why the procedure is standardized
2. 0:08 — 1 mL or 1 g in 500 mL
3. 0:26 — Graduated cylinder and micropipette
4. 0:35 — Tared scale for dry products
5. 0:40 — Initial and final PPM on the 500 scale
6. 0:55 — Initial and final pH
7. 1:10 — Cleaning between products
8. 1:17 — Single-use pipette tips
9. 1:22 — What the result is meant to show

Selecting a timestamp opens the video at that moment without moving you away from this section.

It is 500 mL, not 50 mL

Every product goes into 500 mL of water, as shown in my video. Volume sets the concentration, so use the same amount every time.

Liquid and dry products are reported separately because 1 mL and 1 g are not interchangeable doses. The fixed ratio is a comparison condition—not a recommendation to feed every product at 2 mL/L or 2 g/L.

What the meters are really measuring

pH: acidity at that moment

pH records how acidic or basic the sample is after mixing and settling. It can show that one product pushes low-alkalinity water farther than another. It cannot predict how a buffered tap source, substrate, root zone or complete multi-part recipe will behave over time.

EC: total electrical conductivity

Electrical conductivity measures how readily the solution carries current. Dissolved fertilizer ions usually raise EC, which makes it a useful concentration check. But EC does not identify which ions are present, whether the nutrient ratios are appropriate or how much of each element a plant will absorb.

PPM: an EC conversion, not a lab count

A handheld TDS meter measures conductivity and converts it to a displayed “PPM” value. Different conversion scales produce different numbers from the same EC. HWGrow’s original comparison used the 500 scale, so every result must keep that scale attached. For cross-brand comparisons, EC in mS/cm is the cleaner common language. The pH, EC, TDS and PPM guide explains the conversions.

Step-by-step protocol

1. Record the product. Capture the full name, formula, lot number, manufacture/purchase date and whether it is liquid or dry.
2. Condition and calibrate the meters. Follow each meter’s calibration and storage instructions. Record the calibration standards and date.
3. Control the water. Use the same reverse-osmosis source for a comparison batch. Measure 500 mL in a clean graduated cylinder.
4. Record the baseline. Measure water temperature, pH and EC. If displaying PPM, record the conversion scale.
5. Measure the product. Use a calibrated P1000 micropipette for 1.00 mL of liquid or a tared 0.01 g scale for 1.00 g of powder.
6. Add and mix consistently. Use the same vessel, mixing time, intensity and rest time for every product. Confirm that dry material has dissolved before reading.
7. Measure the final sample. Rinse the probe as directed, record final pH, EC and temperature, then calculate the change from baseline.
8. Prevent carryover. Clean and dry the vessel between products. Use a fresh pipette tip or clean measuring tool for every product.
9. Repeat the run. For stronger comparisons, run at least three independently prepared samples and report the mean plus the observed range.

Data table to publish with every nutrient test

What this test tells me

Reverse-osmosis water makes the baseline clean, but its low buffering capacity can exaggerate pH movement compared with tap water. To understand your actual feed, repeat the measurement with your own source water and use the manufacturer’s labeled dose. Search your ZIP code plus “water report” to find the local utility report, then compare it with your meter and, when needed, a laboratory water analysis.

Recommended nutrient-testing tools

pH and EC meter kitMeasure both the water baseline and the final mix. Calibrate and store each probe according to its instructions.View product

500 mL graduated cylinderMakes the water volume visible and repeatable; read the bottom of the meniscus at eye level.View product

0.01 g digital scaleFor dry products. Tare the vessel and verify the scale with its calibration weight before comparing samples.View product

1 mL measuring syringesA practical home alternative for liquid products. Use one clean syringe per product; a calibrated micropipette is more precise.View product

Affiliate disclosure: HWGrow may earn a commission from qualifying purchases at no additional cost to you. Equivalent calibrated tools can be substituted without changing the test design.

Evidence and measurement references

• University of Maryland Extension: fertilizer EC checks — measure clear water first, subtract the baseline and compare with the product label.
• Penn State Extension: water-quality toolkit — EC estimates dissolved-ion concentration; TDS/PPM is a related conversion and EC is preferred in production.
• University of Missouri Extension: hydroponic nutrient solutions — EC is a proxy for total ions and does not confirm that each nutrient is at the correct concentration.

Use the result in a real grow

This protocol tells you how a bottle changes a controlled sample. For an actual plant, pair it with the complete pH, EC, PPM and runoff guide, the product label and the plant’s response. If two meters disagree or a reading does not make sense, ask HWGrow a question and include the water source, product/dose, meter model, calibration date, temperature and both readings.

HWGrow nutrient-test FAQ

Does the protocol use 50 mL or 500 mL of water?

500 mL. Using 50 mL would make the sample ten times more concentrated.

Is 1 mL per 500 mL a feeding recommendation?

No. It is the liquid-product comparison rate, equal to 2 mL/L. Always use the label, your full recipe, source water, medium and plant response for feeding decisions.

Does a PPM meter count individual nutrient molecules?

No. A TDS meter measures electrical conductivity and converts it to a PPM-style number. It does not identify which elements are present.

Why record the water reading first?

The water already contributes pH and conductivity. Recording the baseline lets you calculate the change associated with the added product.