How to Measure EC & PPM and Grow Healthier Cannabis

What is TDS/PPM?

Dictionary definitions are helpful to a point, but some clarification on PPM and TDS could be useful. 1ppm is equal to 1mg of dissolvable material per liter of water – a tiny, tiny unit of measurement. For reference, most tap water contains somewhere in the range of 10-200ppm, with unfiltered well water sometimes containing up to around 400ppm.

Again, PPM is the unit of measurement. What you’ll actually be measuring is the amount of total dissolved solids in your nutrient solution, which is found by testing the electrical conductivity of the liquid. A solution with more minerals in it conducts more electricity.

What should my PPM be for seedlings?

Seedlings require very mild nutrients to prevent stress. Aim for a PPM of 100–250 and an EC of 0.2–0.5. At this stage, plain water or a very diluted nutrient solution works best. Keep the pH in check to encourage healthy root development.

What should my PPM be during veg?

During vegetative growth, cannabis needs more nitrogen for strong foliage. A PPM range of 300–700 and an EC of 0.6–1.4 is recommended, increasing gradually as the plant matures. Regularly check runoff EC to prevent salt buildup and nutrient lockout.

What should my PPM be during Flower?

As plants enter flowering, they require more phosphorus and potassium. The recommended PPM range is 800–1,600, with an EC of 1.6–3.2.

• Early flower (weeks 1–4): PPM 800–1,200, EC 1.6–2.4
• Late flower (weeks 5–8): PPM 1,400–1,600, EC 2.8–3.2

Be sure to monitor runoff PPM/EC and flush if needed to maintain proper nutrient absorption and improve final bud quality.

How Much Is Too Much PPM & EC for your cannabis plants?

While having the right PPM and EC levels helps plants thrive, too much can cause nutrient burn, lockout, or stunted growth. The ideal PPM depends on several factors, including:

1. Nutrients Already in the Soil

• If you’re growing in amended soil (like super soil or compost-rich mixes), your plants may already have access to plenty of nutrients. In this case, adding extra fertilizers can lead to overfeeding.
• Tip: Test your soil’s EC before adding nutrients to avoid excess buildup.

2. Water Source & Mineral Content

• Tap water often contains dissolved minerals (calcium, magnesium, etc.), which contribute to the total PPM. If your base water is already 200–300 PPM, you’ll need to adjust your nutrient mix accordingly.
• Tip: Use filtered or RO (reverse osmosis) water if your tap water is too high in PPM.

3. Runoff PPM & EC Checks

• Measuring runoff PPM/EC helps determine if salts are building up in the root zone.
• If your runoff PPM is much higher than what you’re feeding, your plants may not be absorbing nutrients properly, leading to lockout.

Signs You’re Overfeeding

🚩 Leaf tips turning yellow or brown (nutrient burn)
🚩 Drooping or curling leaves (overfertilization stress)
🚩 Runoff EC consistently rising without increasing plant growth

How to Fix High PPM/EC?

• Flush your medium with pH-balanced water until runoff PPM drops to an acceptable level.
• Dial back nutrients gradually instead of making drastic changes.
• Monitor plant response—some plants may recover quickly, while others take time to adjust.

Keeping PPM and EC within the right range ensures healthy growth, better yields, and higher-quality buds without excess salt buildup.

The Importance of Measuring EC/TDS/PPM for Growing Cannabis

Since plants are immobile, they can’t gain nutrients by eating and have to rely on osmosis instead. Plants’ roots have semi-permeable membranes that allow nutrient-rich water to flow in up through the stalk to hydrate and nourish the leaves and flowers.

Unfortunately, plants excrete waste salts into the same soil, relying on fresh water to dilute them to a healthy level. 

To make sure you’re keeping your plants healthy, you’ll want to measure the PPM of all the water you give your plants, as well as the PPM reading of your plants’ runoff water. This information will allow you to correct your nutrient levels and avoid over- or under-nourishing your cannabis.

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How and When to Measure TDS and PPM

When you get ready to water your plants, always start by mixing in the nutrients and then adjusting the pH if necessary. After that’s been done, check the solution’s ppm. You should do this every time you water your plants, and record the data somewhere for reference.

You only need to check the PPM of your runoff once a month but some like to do it more often.

Don’t muddy up your measurements

The PPM measurement of soil runoff will be much higher than in coco. Because soil is made up of many different elements they will add to the total measurement. This doesn’t mean the soil is over-fertilized.
When measuring soil runoff PPM you’re looking for trends and not the exact amount of nutrients in the soil. Big changes in the data are what you need to worry about. 

How to Calibrate and Use a TDS Meter

A TDS meter like this one is the simplest way to check your nutrient solution’s PPM. More accurately, it’s a TDS/EC (electrical conductivity) meter. This device measures the electrical conductivity of a liquid in ?S/cm² (microsiemens per centimeter squared) and then multiples that value by a factor of 0.5 to convert the number into PPM. Some meters use a factor of 0.6 or 0.7 to calculate PPM instead, so it’s best to find a meter that is intended to measure bother EC and PPM.

A device like this will allow you to get an accurate PPM measurement quickly and easily – as long as it is correctly calibrated. Most of the time, they’ll be calibrated fairly well out of the box, but it’s best to double-check. All you’ll need is some calibration solution. Check your meter’s instructions for how to manually make necessary adjustments.

Once the TDS meter is calibrated, turn it on and wait for it to read zero, then insert the tip into the tap water or nutrient water you want to test. Then just wait to see what the reading is. Simple as that!