Water is essential for both people and plant life, with cannabis plants being no exception. Prepare yourself as we delve into water quality and understanding water’s relationship with plants. I break down all you need to know about PPM, E.C., monitoring runoff, signs of potential issues, and plenty more to help you on your way to becoming well-versed in all things water and cannabis.
TL/DR | Key Takeaways:
- The optimal E.C. range for flowering hydronic plants is between 1.9-2.4
- The optimal E.C. range for flowering organic plants is between 1.9-2.3
- PPM refers to parts per million and is directly related to your E.C. levels.
- Soft water will have 50–300 parts per million and 0.4 EC.
- hard water will be between 320-420 parts per million and 0.8 EC
- Rainwater will test at 500 ppm, with filtered rainwater testing around 30 ppm.
- Reverse osmosis water will test at 6.0–6.5 pH and show a reading of 20 ppm or less.
- If the EC-related problem is not fixed, eventually, the plant will suffer and die.
- A digital meter reading of E.C., TDS, and PPM is necessary.
- TL/DR | Key Takeaways:
- The Role of PPM, TDS, and E.C. in Cannabis Cultivation
- The Source of Water Matters to Cannabis Plants
- Monitoring Appropriate E.C., TDS, and PPM of Your Runoff Water?
- Common Issue: Calibrating Your TDS, PPM, and EC Pen.
- Conclusion
The Role of PPM, TDS, and E.C. in Cannabis Cultivation
During its life, a cannabis plant depends on a specific set of parameters, including the correct water source, nutrient solution strength, and pH levels. The easiest way to think about it is that E.C. and PPM are real-time data that allow you to control what goes in and comes out of the growing medium.
What are E.C. and PPM?
E.C. stands for electric conductivity and measures how much a material can conduct electricity. Salts from liquid nutrients cause electrical conductivity levels to increase when mixed with water, so the more nutrients in your water, the higher the E.C. will be.
PPM refers to parts per million and is directly related to your electrical conductivity levels. PPM is a measurement that describes the concentration of your nutrients in water or soil. Now, if E.C. levels reference the potency of the nutrient solution, why do I need to consider PPM?
It may be overwhelming, but the best way to think about the relationship is in the same sense as degrees Celsius and Fahrenheit, or miles per hour (MPH) and kilometers per hour (KPH). So your E.C. levels will be a reflection of the parts per million. Just remember, EC and PPM both measure the same thing. The easiest way to keep things sorted is to have a reference table for all the various measurements printed out on your grow room wall!
What are TDS levels?
TDS refers to the level of total dissolved solids in your nutrient solution. Measuring TDS is done using parts per million. All you need to remember is that E.C. determines how well electricity can pass through, and TDS refers to the dissolved solids in the water. Measure PPM and TDS levels using the following calculations:
- E.C x 500 = TDS levels
- E.C x 700 = PPM levels
PPM Conversion chart
CF | EC MS/CM | PPM 500 TDS | PPM 700 (ECx700) |
2 | 0.2 | 100 | 140 |
4 | 0.4 | 200 | 280 |
6 | 0.6 | 300 | 420 |
8 | 0.8 | 400 | 560 |
10 | 1 | 500 | 700 |
12 | 1.2 | 600 | 840 |
14 | 1.4 | 700 | 980 |
16 | 1.6 | 800 | 1120 |
18 | 1.8 | 900 | 1260 |
20 | 2 | 1000 | 1400 |
22 | 2.2 | 1100 | 1540 |
24 | 2.4 | 1200 | 1680 |
26 | 2.6 | 1300 | 1820 |
28 | 2.8 | 1400 | 1960 |
30 | 3 | 1500 | 2100 |
32 | 3.2 | 1600 | 2240 |
34 | 3.4 | 1700 | 2380 |
36 | 3.6 | 1800 | 2520 |
Visible Signs of E.C., TDS, and PPM Issues on Your Plants
To make this as simple as possible, it’s all about nutrient levels. Low E.C. levels will mean the plants are drinking more nutrients than are available. High E.C. levels can become uncomfortable for plants. It can also lead to nutrient toxicity (nutrient burn), severe stress, and death in the worst-case scenario.
Below are some signs that you may suffer from low E.C-related issues
- Plants will begin to suffer nutrient deficiencies within a short time frame.
- Leaves will turn yellow with brown tips as the first signs of a nutrient shortage.
- The growth rate of the plants will gradually slow down, causing the leaves to wilt.
- Plants cannot access the optimal nutrients, resulting in lower yields.


Below are some signs that you may suffer from high E.C-related issues.
- Plants can experience severe tissue death and necrosis due to high E.C. levels.
- Leaf coloration can turn pale green, with the outer edges turning brown and lifeless.
- The entire leaf tip can turn fully brown and die off in a short amount of time.
- Foliage will display chemical burns, turning the tips of the leaves bright yellow.
- Over time, the leaves will become wilted, brown, and brittle.
- The plant will eventually suffer and die if the E.C. problem is not fixed.


Measure Often to Avoid Salt Build-up and Nutrient Lockdown
The golden rule to being a great grower is to measure often to prevent salt build-ups, nutrient lockouts, and a world of problems that may arise later. E.C. and PPM issues can be deadly serious, with the ability to wipe out a crop quickly, leaving an uneducated grower very little room to recover!


The Source of Water Matters to Cannabis Plants
Hard water contains high levels of minerals like calcium and magnesium, while soft water has fewer minerals and feels gentler on the skin. However, you can use your measuring device or ask your local water provider for details. According to the U.S. Geological Survey (USGS), water is defined as soft when it contains 60 mg/l (60 ppm) or less of specific ions. Conversely, water with more than 120 mg/l (120 ppm) is classified as hard, while values in between these ranges are considered moderately hard.
Water Hardness | TDS (PPM) | Grains Per Gallon (GPG) | Calcium Carbonate (mg/L) | EC (μS/cm) |
Soft | 0-60 | 0-3.5 | 0-60 | 0-100 |
Moderately Hard | 61-120 | 3.6-7.0 | 61-120 | 100-200 |
Hard | 121-180 | 7.1-10.5 | 121-180 | 200-300 |
Very Hard | 180+ | 10.6+ | 180+ | 300+ |
Before we cover the different available water sources, it is important to know that the information below are approximate figures. You should always check your own measurements.
Soft tap water
Soft water will have a pH level between 6 and 7, and when tested with a TDS pen, the PPM levels will be between 50 and 300 parts per million and an E.C. level of around 0.4.
Hard tap water
The pH level of hard water will be around 8.5 (so using pH down is necessary). Your TDS meter will reveal the PPM levels are between 320 and 420, effectively meaning the E.C. will be significantly higher than a soft water reading of 0.8 EC.
Reverse osmosis water
Reverse osmosis water will test at 6.0–6.5 pH, your TDS meter/pen will show a reading of 20 ppm or less, and the E.C. levels will be zero. It is worth knowing that the downside to filtering water using a R/O filter is the returns of clean filtered water. It’s a slow process that takes time. Unless you are flushing your plants before harvest, giving them R/O water alone is never advised due to the lack of available nutrients, especially secondary nutrients such as Calcium (Ca) and Magnesium (Mg).
Rainwater
Rainwater can be acidic depending on the atmosphere, pollution, and carbon dioxide levels. Its pH can be tested between 5.0 and 5.5, with 0.4 EC, meaning TDS meters should show 500 ppm. Filtered rainwater tests around 30 ppm.
Monitoring Appropriate E.C., TDS, and PPM of Your Runoff Water?
Salts in the nutrients will naturally build up around the roots and the growing medium. However, salt build-ups can have an adverse effect and cause pH levels to change, causing nutrients to become locked out and subsequently unavailable to the plant.
As a result, the imbalance in E.C. and pH will cause a negative ripple effect. My best advice is to check everything using your hand-held digital EC meter and pH pens. Measure often and always be one step ahead when it comes to feeding your cannabis plants the correct way.




What Tools Do You Need to Measure E.C. and PPM?
You should buy a TDS pen or digital meter that can read E.C., TDS, and PPM. Some of the pens available online can do all three (including pH), while others are specific to one value.


How to Analyse the Results of Monitoring E.C. and PPM
This simply means you will need to obtain a reading of the nutrient solution before giving it to the plants and then one from the solution runoff afterward. This creates a system that shows, in real time, how many nutrients the plants use.
The outcome of checking your runoff will be one of three: the runoff will be lower than the original E.C. level, the runoff will be the same, meaning everything is just right, or the runoff will reveal a higher E.C. level.
What is the Ideal PPM, E.C., and TDS for Cannabis Plants to Thrive
The Ideal PPM and EC ranges for hydroponics
Lifecycle | EC Levels | PPM | TDS |
Seedling stage | 0.7-1.5 | 490-1050 ppm | 350-750 |
Vegetative stage | 1.6-1.9 | 1120-1310 ppm | 800-950 |
Flowering stage | 1.9.-2.4 | 1310-1680 ppm | 950-1200 |
Flushing stage | 0.8 | 0-560 ppm | 0-400 |
The Ideal PPM and EC ranges for soil
Lifecycle | EC Levels | PPM | TDS |
Seedling stage | 0.8-1.3 | 560-910 ppm | 400-650 |
Vegetative stage | 1.2-1.9 | 840-1310 ppm | 600-950 |
Flowering stage | 1.9.-2.3 | 1310-1610 ppm | 950-1150 |
Flushing stage | 0.8 | 0-560 ppm | 400 |
How to Achieve the Right Levels of PPM, TDS, and E.C.
So, you have done all your testing and are now ready to compare the data!
In the event, the measurements are the same:
This is a good indicator that the plants are eating up the nutrients without being short of food or overfed. As far as E.C. and PPM are concerned, you do not need to change anything at this point.
When the measurements are lower than what went in:
This means you need to gradually increase the strength of the nutrient solution, as the plants use them quickly. Some strains will be different, so be open to the idea that some plants will use more or less than others during the vegetative and flowering stages.
In the event, you see measurements that are much higher than what went in:
Stay calm, but you may have salt buildup. With this level of nutrient concentration, undissolved salts can build up around the roots and the growing medium. I recommend feeding only water with enzymes and testing the runoff. Keep doing this until the runoff E.C. and PPM readings return to their comfort zone.
Case Study Example
I remember visiting a friend who bought a new brand of coco coir, so I advised them to check the runoff from the coco. To our surprise, the runoff tested a staggering 2.8 E.C. We resolved the issue by washing the coco with enzymes and water until the pH levels were between 5.5 and 6.0 and the new E.C. level was between 1.0 and 1.3.
Now let me explain why using this coco coir would be problematic. The substrate was so rich in salt that the seedlings and clones would have struggled to settle and develop roots. Adding any nutrient solution would have caused the E.C. levels inside the growing medium to have skyrocketed. Nutrients would have been locked out, causing a ripple effect and further nutrient deficiency issues. Without soft water or reverse osmosis (due to the E.C. being so low), maintaining a comfortable E.C. level close to 1.2 would be difficult.
Stoneys Pro Tip: A Note on Enzymes
Enzymes are a superb addition to any garden from the seedling stage until harvest. They will increase nutrient uptake and availability, accelerate the decomposition of organic matter, break down dissolved salts in coco coir, and keep roots sparkling white in hydro systems. You can always try to combine multiple enzymes at once. I recommend Cannazyme, Sensizyme, Hydrozyme, Powerzyme, and ATAzyme products.
Common Issue: Calibrating Your TDS, PPM, and EC Pen.
The most common problem I encountered when speaking with beginner growers was calibrating their E.C., pH, and TDS meters and pens. Calibration is extremely important; if not correctly done, it will only result in incorrect E.C. and PPM levels. I strongly recommend learning how to properly calibrate your EC meters, PPM meters, pH meters, and TDS pens by following the instruction guide and using calibration fluid. If you need more information, take a look at Bergman’s Growbible below.
Conclusion
The easiest way to digest everything many consider technical is that pH, E.C., PPM, and TDS are all closely related. The two most important things to know are that your plants need optimal pH levels to absorb nutrients, and the potency of your nutrient solution should be in the ideal range.
With the aid of your digital pen or pens, there is no reason why you cannot control the exact amount of nutrients your plants receive. Overfeeding results in high E.C. levels, and the risk-to-reward factor can lead to stunted plants, low yields, and clear stress on the leaves and foliage. Enzymes are my favorite way to control the amount of salts in the growing medium; however, I suggest checking out Robert Bergman’s Grow Bible and seeing what the main man has to say about the matter! Otherwise, good luck learning the language of water and producing some phenomenal flowers.
I do a lot of nutreint maping and most nuts when following schule will end up very acidic.I know what most of my nuts do in the water.L believe you should write an article about this as alot of people I know think if the water they use is ok then they believe it,s ok.wrong.I use drops instead of my meter,fast and accurate.
Hey chink,
Your comment is a bit unclear. I would like to say that I do not believe that most soluble nutrients range acidic. First we will start with the water. ultimately the water is going to determine the final PH of any solution mix. If you have high PH water or alkaline water above 7.0, then you will end up with a PH that has to be adjusted down. Low PH or acidic water will possibly remain in the proper range once mixed with water soluble nutrients or minerals (as I do in the greenhouse).
Thanks for your comments.
PPM is defined as Parts Per Million of (Something) dissolved in the liquid you are measuring.
Unless you have access to a gas chromatograph in order to measure what exactly is making up your PPM, then the best measure is to rely on pH for proper nutrient uptake. See the previous posts here for the proper hydro or soil pH (5.5 -65.) Measure the pH of your nutrients (add the x tsp/gal and then check the pH) and adjust. Then water and check the runoff pH and readjust as necessary.
It’s a balancing act…
Yirgach,
Thanks for sharing 🙂
What’s the relationship between PPM and the feeding schedule provided by the nutrient manufacturer? I’ve used the Fox Farms “main 3” lineup for my first 3 plants and have followed their schedule (starting at quarter strength), but I’m curious if I should ignore the dosages in the feeding schedule and rely solely on PPM instead?
Dan,
You can do it wither way. I teach some growers to use the directions on the bottle because a multi-million dollar company did the research and advised you to follow their feeding schedule (sometimes different than guidelines on the bottle).
On the other hand I also teach the ppm method of using less and building ppm strength as the plant gets bigger and then as flower develops. You can use 400-600 for seedling bumping to 800-1000 in late veg, and then run 1000-1200 during flowering with a boost of Potassium (K) 2-4 week before estimated harvest date.
Hope this helps, 🙂
I’ve been researching urine as a fertilizer for plants, this might sound gross but I’ve been drinking a diluted urine solution to help my HEP C. Would adding a diluted urine solution to my plants help them grow?
Aaron Keith O’Brien
Aaron Keith O’Brien,
Personally, I would not use as urine solution unless it was a last resort. If you already have a nutrient regimen, merely adding urine is not going to give you much of an advantage in the long run. Might be useful in an “off grid” situation or if you run out of nutrients but, in general it is OK but, not recommended in general.
Happy growing
My water comes out of the well at around 427 ppm. Is that a problem? If so, what should i do about it? ( if it matters, i plan to grow hydro/bubbleponics)
Dan first thing is to filter your well water to lighten the PPM then replace said PPM with nutrients based PPM however you filter it is your call but at 427 theres no room for anything else for your babies other than the calcium and iron from the well. I might advise a whole house filter and then a finer micron filter for your plants water.
wowrich42065,
My thoughts exactly. Thanks for sharing. 🙂
Dan, Sorry wee missed this but, for future reference. If your ppm of tap water is 427; I would invest in a small Reverse-Osmosis unit 4-5 stage approx. 100 bucks on e sites.
Happy growing
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[…] If you can drink it so can your marijuana plants. Professional growers use corrected water with pH between 5.5 and 6.5 and EC between 1.8 and 2.2. There are 3 common methods for testing these […]
Different nutrients break down at different PH levels. With that said, can you fluctuate your PH from 5.5 to 6.8 through out its cycle in order to break down the right nutrients at the right stage when using hydroponics?
Please advise, Thank You!
jack kirkendall,
Different minerals are more available in certain PH levels. They are all available at proven pH of 5. for Hydroponic grows, and 6.5 in Soil grows.
NO you cannot and should not fluctuate your PH from 5.5-6.8 unless you want to lock out some minerals causing issues with your plants.
You need a consistent PH in order for the plants to use their energy to thrive.
Denny,
nuts = mutes; I suppose. It is best not to abbreviate when asking for grow advice.
1. It is not advisable to add nutrients to new plants in Sunshine soil. Nutrients should be held back until the transition/flower phase of the grow.
2. You could be over watering because, there is no scdeule to water soil, other than when the plant medium is dry. By watering small plants every other day; You may be drowning the roots.
3. Optimum PH for soil grows is 6.5
Between the 3 it is hard to diagnose your issue because, both mistakes can cause leavers to yellow. This is where I would start looking, though.
I Started out with very few Nuts in sunshine # 4 soilless mix and plants were about 8″ tall total green and then started to turn a little yellow a few leafs. I was watering every other day with 5.8 pH led lights about a foot above the plants Humboldt–micro, Grow , bloom mix. After seeing the yellow leafs I increased the nuts at around 600 then cut back to 450 PPM total including the well water. It looked like burn yellow leaves brown tips curling up and down.? I checked my well water and it says 258 PPMs so I went to plain 5.9 pH well water. Everything is still the same. Then I cut the nuts in half. Still the same. Now I’m back on plain well water pH 5.9 still the same. This is over a month or so and I can’t figure it out. The plants are mostly yellow I now ordered an osmosis system thinking maybe it’s the well water? Anyone have any other thoughts? Thanks Denny
Nutrients are in all food, and available to all living beings. Life and photo synthesis cannot occur without proper nutrition.
This article treats nutrients like they are a food source and that is not true. One does not want to think of fertilizers as food. Plants are Autotrophic meaning they make their own food. The fertilizers are more like vitamins. Too much and you will hurt the plant.
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For hydro, Ph range goes from 5.5 to 6.5… so 5.9 or 6.0 is the goal for the whole cycle.
650 PPM in first vegettive week , increasing by 50 every 7 days.
I’ve read if using PPM one can go as high as 1800 PPM, and read some use as high as 2800 PPM?
Whats’ up with that?
Jack. You can go that high a nutrient concentration. You will never get the chemical, or fertilizer taste out of the plant. 1000-1500 ppm is all you need to grow really nice tasty plants.
[…] Although hydroponics systems can sometimes support a cannabis plant with a pH of as low as 5.5, the ideal range is somewhere around 6. Read more about ph levels […]
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150 ppm is a very light nutrient solution. Joining the support forum and asking questions will get you the opportunity to access much more info. I look forward to helping you out there. lw
20 ppm is great for watering your plants. 🙂 Have you go a nutrient schedule planned for your plants? Perhaps it would be great, if you joined the Support forum.
I have rainwater with 20ppm to watering my plants is good idea add nutrients to reach 150ppm
Hi. Help needed.
I have young seedlings in a hydro system. What are the recommended ppm levels?
Any info will be highly appreciated.
Hi Dan,
For hydro you can start with 500 ppm and increase with 50 every week. And make sure you keep the pH level of your medium around 5.5
Robert
If starting out @ 500 ppm having only 4 wk. of grow & 4 wk. of flowering using auto-flower with hydroponics whats’ the max?
Also, if using EC not ppm what numbers are used?
TX Jack
This is the absolute most important information you need to understand to grow healthy plant over and over again. Knowing how to read and adjust the PH of your plants is imperative.
When it come to EC/PPM; It is very important to know that sometimes, “less is more”. Don’t over0fert your plants because you are impatient and want to see them get bigger over night. Learn how to measure your run off in soil, or your res PH in hydro. Get ahead of the game.
Happy growing