What Is the Perfect PPM for Weed? | How to Measure It & Achieve Optimal Levels

You might be wondering how to give your weed plants the right amount of nutrition.

What is the perfect PPM level for weed? Are you feeding them well, or are you not feeding them well enough?

It’s hard to say when you don’t know where to begin. Well, this is the place to start.

This article will guide you in measuring the PPM levels and what level is perfect for achieving the highest yield. Read further to know more!

What Is PPM?

PPM stands for “Parts per Million.” This measurement is the mass of a chemical or contaminant per unit volume of water.

It can also be expressed as milligrams per liter (mg/L). In simple terms, PPM is the smallest part of a bigger whole.

In cannabis cultivation, PPM levels measure nutrients in the water you feed your weed plants. 

There are minerals in the tap water or nutrient-rich water you prepare before watering your weed plants that can be measured in parts per million.

Why Is Measuring PPM Important?

Measuring the PPM is vital in growing cannabis plants.

You must know the nutrient levels of the water you will use because these can significantly affect the plants’ growth.

Weed plants are EXTREMELY sensitive to proper nutrition. High nutrient concentration can cause a nutrient burn.

That is why you MUST ensure you’re feeding them optimal nutrition without the risk of nutrient deficiencies.

Everyone in the cannabis industry knows how important this is!

The Different PPM Results

Once you have the PPM results, you can make proper adjustments to get it in the desirable range. You can do this by simply adding nutrients suited to your plants’ needs.

What do you do with the different PPM results? You either increase or decrease the nutrient levels depending on each situation.

No PPM Change

You should be CONCERNED if the TDS meter shows no difference in PPM results between your nutrients and your runoff.

No difference in PPM results means less nutrient level intake.

That would mean your plants are not taking enough nutrients as they should!

To solve this, check the pH level of the soil. Inconsistency of pH levels may hinder plants’ nutrient intake.

PPM Lower in Runoff

The ideal result is a low PPM runoff reading compared to the nutrient’s PPM. When you check the PPM regularly, observe any significant decrease in the runoff results.

If your ppm drops from 1500 to 800 daily for a week, your plants consistently absorb nutrients at the same level.

You can gradually add more nutrients if the PPM meter shows extremely low runoff levels. Make sure you add nutrients ONLY when needed to avoid nutrient burn.

Lower-Than-Usual PPM in Runoff

If you’ve significantly increased the nutrient levels and the PPM runoff results are alarmingly lower than usual, that can be a nutrient LOCKOUT! But don’t panic. It’s easy to fix.

A white precipitate buildup in the reservoir water might be the reason for this. To fix it, mix the nutrients properly as you add them and wash your mixing cup between nutrients.

Water PPM Higher in Runoff

Water PPM runoff higher results are uncommon but can still happen.

This happens when there’s a buildup of salt in the plant’s root zone. It gets stuck and dissolves into the runoff.

The culprits for this salt buildup are:

  • Calcium phosphate
  • Calcium carbonate
  • Calcium hydroxide

As a result, ppm levels in the runoff increase.

How do you fix it? Flushing with water can help remove the calcium salt buildup. But before that happens, make sure you mix them well.

Yellow Leaves

If your cannabis plant has yellow leaves, check the PPM results for your reservoir water and runoff. This could be due to nutrient deficiency.

If the nutrition levels are significantly decreasing between your reservoir and runoff, yellow leaves are not caused by nutrient deficiency. It could be the pH level.

Ensure that you check the pH and PPM regularly.

Organic Soil

The PPM reading for testing organic soil can be difficult to decipher compared to using synthetic fertilizers. Organic soil contains complex molecules that can turn into simple salts.

With this, your soil’s PPM readings won’t consider the total nutrients that have yet to break down. This will make the PPM reading UNRELIABLE.

In this case, you need to pay more attention to your pH levels and signs of possible nutrient deficiencies.

pH Changes

The significant pH changes are known as pH drift. Changes in pH can prevent the roots from absorbing nutrients. In cannabis cultivation, they call this NUTRIENT LOCKOUT.

A little discrepancy between pH levels is normal if they’re in the correct range.

We need to emphasize the importance of checking the pH and PPM regularly for this reason.

How Do You Measure PPM?

If you want to measure PPM in the water you use for growing marijuana plants, you will need a TDS meter. This will accurately measure PPM so you can keep your plants healthy.

Measure the PPM in 4 simple steps:

Step 1: Prepare the Water You Want to Test

Decide which water you intend to use for your marijuana plants. If you plan to make nutrient water, make sure you test it before watering your plants.

As much as you want your plants to grow healthy, you MUST be precise with the amount of nutrients you give them. Too many nutrients can cause a nutrient burn.

Step 2: Calibrate Your Meter

You will need to calibrate your meter. To do this, you will need to use a calibration solution. After calibrating your TDS meter, turn it on. Make sure it is reading zero.

This way, you can be sure that the reading is accurate. A tiny error can MASSIVELY impact your plants’ growth.

Step 3: Test Out the Water

When everything is set, you can test the water by putting the tip of the meter in it. There should be a reading in a few seconds.

Step 4: Understand the TDS Reading

It’s time to interpret the TDS reading. If you’ve tested out tap water and the results come back as 200-300 PPM, it is in the normal range.

However, plants’ PPM levels will vary as their growth progresses. You will have to adjust depending on each stage.

In most feeding charts, these are the PPM ranges from seedling to end of the flowering stage:

  • Seedlings: nutrients aren’t needed during this stage
  • First half of the vegging cycle: 350-700 ppm
  • Late vegetative stage: 700-1000 ppm
  • First half of flowering stage: 1000-1250 ppm
  • End of the flowering stage: reduce to 0-600 ppm

What Are the Different Tools for Measuring PPM?

If you plan to grow cannabis plants, you will need two different tools for PPM measurement. These are EC and TDS meters.

Both EC and TDS meters are used for testing the water quality.

TDS Meter

A TDS Meter is a small hand-held device that indicates the “Total Dissolved Solids” in a solution.

TDS meters may be referred to as TDS testers or PPM testers, but all of these are different names for the same thing.

You can purchase many TDS meters for as low as $10, but more advanced models can cost $1,000+ depending on the level of accuracy and additional features offered.

A basic TDS meter may only measure the amount of total dissolved solids or certain nutrients in a solution. This is fairly its primary purpose.

On the other hand, other advanced TDS meter models may be able to check salinity, temperature, and more. 

EC Meter

An EC meter measures the electrical conductivity of the water sample. EC meters can be used in the field to measure water directly.

EC or Electrical Conductivity is the capacity that liquids have for transporting electricity. For example, the water conductivity factor depends on the amount of minerals in it.

It can conduct electricity like copper wire if it has a good amount of minerals. However, distilled water (H2O) won’t conduct anything.

With the help of an EC meter, you can easily check the amount of nutrients in your water source.

What Are the Different Types of Water for Cannabis Plants?

Understanding the best water cannabis plants need is a FUNDAMENTAL factor. Good water quality is not enough.

Water quality depends on how you treat your water source. Here are the different types of water for your weed plants:

Tap Water

Most tap water in certain countries has chlorine to kill microbes and bacteria that are DETRIMENTAL to humans and even to plants.

Using unfiltered tap water on cannabis is not a death sentence for plants. This type of water varies greatly depending on the municipality and water treatment protocols.

If you intend to use tap water to grow cannabis plants, make sure you remove chlorine by letting the water sit in your reservoir or bucket for a day or two.

If the PPM is too high after you test it, you can lower it with carbon filtering.

Bottled Water

Bottled water, like drinking water, is an uncontaminated pure water source relatively inexpensive for a small-scale garden.

What’s good about this soft water is that it is affordable in low quantities and easy to source. It’s also safe for plants and doesn’t need any extra filtration.

But in most cases, this lacks the vital root-feeding microbes beneficial for the plant’s root system. You’ll have to make more adjustments.

Rain Water

To collect rainwater or greywater, you can create a system. These systems work best under the right circumstances. On top of that, it can be both inexpensive and eco-friendly.

Rainwater and greywater catches tend to last long periods with little maintenance and can be scaled for any size garden.

This is incredibly convenient to use in climates with dry periods where water saving is encouraged.

Although this system can be inexpensive, it must be filtered and stored correctly. This means this requires filter systems and specially graded storage containers.

Storage containers to use must be those that are built to withstand the elements without risk of contamination or breaking.

Distilled Water

Distilled water is purified water achieved by boiling water away and then condensing the vapor. This water is completely free of all micronutrients vital to plants.

This water is like reverse osmosis water, which lacks minerals. Choosing this water type for growing marijuana is NOT CHEAP, but it guarantees your plants get the proper nutrients.

You won’t have to use a reverse osmosis system for this or test the water PPM, not UNLESS you live in an environment where you have natural, hard, well water from the tap.

Many growers like to use reverse osmosis (RO) or distilled water for cannabis to be safe because it’s pure, clean, and straight.

This is an excellent starting flat base because you can add the plant’s requirements without filtering it.

Depending on their preferences and plants, many growers also temper RO water using tap water to get other macro and micronutrients back in it.

Frequently Asked Questions

We’ve discussed the essential information about PPM and how to measure it.

Refer to the frequently asked question for more substantial ideas about PPM and pH measurements:

What Are the Best pH, TDs, and EC Values for Marijuana Plants?

The optimal pH and EC values are contingent upon three factors:

  1. The growing substrate
  2. Nutrients
  3. Water

For soil growers, a pH of 6.0-6.5 is perfect.

While growers using hydro and coco should aim for 5.8pH, or at least maintain pH around 5.5-6.1.

The recommendation for TDS is below 640 ppm for best results.

This is because hydroponic and soilless cannabis cultivation tends to show higher sensitivity to pH fluctuation and salt buildup when TDS exceeds 200 ppm (500 scale) or 0.4 EC.

What Should My Runoff PPM Be in Soil?

To get a clear picture of what the runoff PPM should be, ideally, the PPM or EC reading of your runoff should ALWAYS be lower.

Depending on your plant’s maturation and the number of nutrients it can absorb, the ppm should range from 750 to 1500 ppm.

This is an indication that your plants are taking up nutrients as intended.

If your PPM/EC readings are extremely low in your runoff, it’s a sign you need to up your nutrients.

If there is no change in PPM or electrical conductivity between your nutrients and runoff, something is wrong, and plants are not feeding as they’re supposed to.

Why does this happen? Spikes or drops in pH usually cause this.

In contrast, if the PPM/EC reading is higher in your runoff than in your nutrient solution, you’ll likely be dealing with a buildup of salt around the roots.

How to Fix It

To deal with this, you’ll want to use an enzymatic line cleaner to clean your plants’ roots.

Line cleaners remove any kind of nutrient buildup, or you can also use filtered, pH-neutral water to flush your roots. Just keep in mind that this process takes multiple attempts.

How Can I Adjust pH Levels?

There are several ways to check the pH of the nutrition in hydroponic systems or a growing medium.

One way is by using pH meters. Adjust to the desired pH by following these steps:

  1. Add any needed supplements to your water
  2. Stir your water to mix it well so it will dissolve faster
  3. Test the pH using your pH meters
  4. Adjust pH by adding “pH Up” or “pH Down” solution (depending on what is needed)
  5. Test the pH again to make sure you get the suitable pH range
  6. Feed the plants with pH-adjusted water
  7. Check the pH of runoff water and water PPM to make sure it’s in the proper range

Will Total Dissolved Solids From Water or Nutrient Solution Affect Your Plant?

Dissolved solids from water can SIGNIFICANTLY affect your marijuana plant.

Regardless of the water quality, it is the TDS levels that matter.

This is why we measure the PPM of the water and pH ranges of the soil to ensure that our plants grow healthy by getting the proper nutrition from both elements.


By now, we hope you already know what the perfect PPM is for your weed plants. Once familiar with those, it will be easy to adjust the levels.

You will be confident that you’re feeding your plants the precise amount of nutrition from seedling to late flowering stage until they’re ready for a FULL and healthy harvest.

You won’t need to invest in many TDS meters or EC meters. You’ll ONLY need one of each. Better yet, invest in the latest versions where you can get a 2-meter-in-1!

Always give your plants the right nutrition — not too much nor too little. That’s the formula for the perfect PPM for weed.