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If you plan to grow cannabis, or even if you already have a few successful grows under your belt, sooner or later you’ll encounter the acronym “ppm”.
While it’s not usually necessary to obsess about ppm and you can grow outstanding cannabis without even knowing what ppm is, it pays to educate yourself about it because it can impact your grow—especially as you advance with your cultivation methods and technique.
Learning more about ppm will put you at an advantage.
What is PPM in Water
So, let’s lift the veil of mystery over what ppm is and how it can relate to growing cannabis. An acronym for “parts per million,” ppm relates to water solubles, including mineral and other substances, in the cannabis space. One part per million equals 1 mg of solubles for every liter of water.
This is a very small measurement increment. Parts per million are found in most types of water, from tap water to mountain spring water. Distilled or reverse-osmosis water are two of the only types of water that eliminated ppm. If you have your tap water tested for purity, the results will be measured in parts per million.
Analyzing your tap water will indicate if you would benefit from a water purification system for drinking water. Testing well water is especially useful because it’s devoid of fluoride and other additives found in most city water to minimize contaminants.
Most tap water that’s safe for drinking or cannabis use will have ppm in the 200-300 range, which is relatively normal. When water gets to several hundred parts per million, it indicates the pipes in your home may be somewhat old and an alternative water source may be beneficial for your cannabis.
How Do You Measure PPM?
To determine the level of ppm in your water, you will need a TDS meter (TDS is an acronym for “total dissolved solids”). So, if you use a TDS meter to measure your home’s tap water and your results come back as 200-300 parts per million, it means you have 200-300 parts per million of dissolved minerals in your water, which is in the normal range.
PPM and EC
Any serious conversation about ppm will also touch on ec; it almost seems inevitable since the two are closely related. EC stands for “electrical conductivity.” Using an EC meter measures the electrical conductivity in the water you’re using, and this reading is useful for measuring the amount of dissolved solubles in your water. A PPM meter and a EC meter essentially do the same things.
As a matter of fact, some TDS meters actually determine the level of electrical conductivity of a water sample and convert the results to parts per million. Simply stated, some TDS meter are really EC meters. Since the two are so closely related, brief mention must be made about EC.
PPM Relevance to Cannabis Cultivation
By this time, you may be wondering why knowing about ppm is important when growing cannabis. The main reason is to provide optimum nutrient amounts to your plants, while simultaneously avoiding burning them by overdosing them on nutrients.
If you’ve grown cannabis long enough and use a variety of fertilizers and soil additives, you realize that all fertilizers are not created the same and nearly every cannabis grower has a favorite. No one likes to see the telltale curled leaf tips and yellowing commonly associated with nitrogen burn in cannabis.
Although plants will eventually recover and be none the worse for wear over the long haul, burning does shock the plants and temporarily hamper them.
Eliminating nutrients altogether for a while will solve the problem, but as the old saying goes, “prevention is the best medicine.” Try to avoid burning altogether by being somewhat conservative with nutrients and additives (use one half to three quarters the suggested amount), and as a second step you can monitor the parts per million to dial in on precise nutrient dosing.
Water PPM and Nutrients for Cannabis
Since water ppm varies depending on the source, knowing the water’s soluble ppm right out of the tap will aid a grower when deciding how much nutrients to add to the water. Along with proper water pH, optimum ppm levels after adding nutrients can sometimes make the difference between adding too little fertilizer or too much. A person with a high tap water ppm can sometimes unintentionally burn a plant when following correct nutrient dosage and schedule protocol.
Plants can only absorb a certain amount of solubles and minerals, and you want your plants to receive the optimum amount.
A young seedling or a cutting (clone) will enjoy a ppm of approximately 500-600 and will respond positively to an increase of about 850 ppm during the medium and late stages of vegetative growth.
During the flower stage, optimum parts per million rises to 1000-1100. Clearly, cannabis plants enjoy increased parts per million as they grow.
Water ppm readings have applications for both hydroponic and conventional soil cultivation methods. With soil cultivation, the water ppm should be checked after adding additives to the watering vessel. For hydroponic use, check the reservoir. With too low ppm, add more nutrients, and with too high, dilute with water until you reach an optimum level.
Like humidity meters, temperature gauges, and pH meters used for cannabis cultivation, there is a wide range of TDS meters on the market at affordable prices. TDS meters that measure parts per million differ somewhat. Some can read a higher level of ppm and can monitor other things like temperature. The range of measurable ppm on some of the fancier meters can go as high as 9999 ppm, but this is not necessary for cannabis cultivation. Using a TDS meter that goes to 3500 parts per million will serve your needs just fine. Anything over 5000 is unnecessary.
Before using your TDS meter to measure ppm in water, nutrients, and runoff, you’ll need to calibrate your device using a solution containing a certain level of ppm. Calibrating solutions can be bought online or at a grow supply store. Make sure your calibration fluid is at room temperature to avoid discrepancies. Follow the package instructions to test your fluid with your meter. If the ppm reading is correct, your device is calibrated. If not, follow your device’s instructions to calibrate it.
Now that you know your TDS meter is up-and-running and precise, you can start using it to measure your ppm. Turn on your TDS meter, remove the cover from the bottom, and ensure it has a reading of zero before inserting the tip (about half an inch) of the meter into the water you’re testing. Below, you’ll find a list of the best TDS meters for your cannabis grow:
- HM Digital TDS-EZ Water Quality TDS Tester
- HoneForest Water Quality Tester
- Generic Digital LCD TDS Meter Waterfilter Tester
- Lxuemlu TDS Meter Digital Water Tester
- Health Metric Professional TDS PPM Conductivity Meter
Understanding PPM Results
To determine the exact nutrient intake of your cannabis plants, you’re going to have to measure the ppm of your nutrient reservoir and your runoff. Generally, the ppm reading of your runoff will be lower than the ppm from your reservoir. This shows that your plants are taking in nutrients when you’re feeding them.
As you can see understanding water ppm for cannabis is a key to getting cannabis grows right! PPM in water is a science in itself.
PPM Lower in Runoff
A low ppm runoff reading compared to the nutrient’s ppm reading is ideal. Keep measuring your ppm regularly to catch any significant drops. If your ppm drops from 1500 to 800 every day for a week, it means your plants are consistently drawing in the same level of nutrients.
For extremely low runoff levels, however, consider increasing your nutrient treat rates gradually.
No PPM Change
If there is no difference in ppm results between your nutrients and your runoff, we have a problem. That means your plants aren’t taking in the right level of nutrients. If this is occurring in your garden, consider checking your pH levels. Inconsistent pH levels can hinder nutrient intake. Nitrate and phosphate, for example, are best absorbed in certain pH ranges.
Lower-Than-Usual PPM in Runoff
If you notice lower-than-usual ppm readings in your reservoir, you may be losing out on nutrients due to nutrient lockout. Check for a white precipitate build-up in your nutrient reservoir. This can occur when some ions don’t mix well together and form a solid. Calcium phosphate is notorious for this.
To overcome this issue, make sure you’re properly mixing your nutrients as you add them and wash your mixing cup between nutrients.
Water PPM Higher in Runoff
A higher-than-normal ppm result from your runoff is rare, but this indicates that there’s a salt buildup at the root zone. The buildup gets stuck and gradually dissolves into the runoff leading to high ppm levels. Ensure you’re properly stirring calcium salts such as calcium phosphate, calcium carbonate, and calcium hydroxide. A line cleaner or flushing with water can help remove the calcium salt buildup.
If your cannabis leaves are turning yellow, you’ll need to check your ppm results for your nutrient reservoir and your runoff. Ensure your nutrient levels (phosphates, nitrates, and potassium ions) are decreasing between your reservoir and runoff, showing that the yellowing isn’t due to any nutrient deficiency. Check for other element deficiencies. If nutrients aren’t the problem, your pH may be the source of the issue.
Is there a considerable pH increase or decrease between your nutrient reservoir and your runoff? A little discrepancy between pH levels is normal. Significant pH changes, however, are known as pH drift. Check for nutrient lockout, one of the main culprits for pH drift. Changes in pH can prevent the roots from absorbing certain nutrients, which is why it’s so important to regularly monitor for this.
Using Organic Soil
Testing your ppm can get tricky if you’re growing organically. Unlike using synthetic fertilizers, organically-assembled soil contains complex molecules that are gradually released over time. Because the organic soil has yet to break down the complex molecules into simple salts, your ppm readings may be hard to decipher.
Ppm readings from your organic soil won’t take into account the total nutrients in your soil that have yet to break down. When growing organically, pay more attention to your pH levels and signs of nutrient deficiencies or imbalances.
Is Measuring Water PPM Necessary?
Whether or not a TDS meter is necessary when growing cannabis depends on your water source and your cultivation goals. Certainty commercial operations should monitor it closely to maximize yield. For the private home grower, the decision depends on how much the grower wants to dial in on perfect cultivation methods and perfect his or her craft.
Measuring the salt and nutrient levels in the water is crucial to ensure the right amount of nutrients are fed. For instance, if you measure your ppm one day and get a result of 1,600 ppm and then measure your ppm the next day and get a 2,100 ppm reading, you know you added too many nutrients the day before.
There is no doubt that many cannabis growers have cultivated and harvested a large number of dank and sticky grows without giving parts per million a second thought. These same growers can grow outstanding bud without worrying excessively about grow room CO2 levels.
When it comes to cultivation factors like ppm and CO2 levels, we’re looking at somewhat advanced procedures. These are choices that separate the novice cannabis grower from the advanced cannabis grower.
If you merely want to grow some good flower for personal use, you may want to skip it. On the other hand, if you want your grow to be as perfect and productive as possible, it would be wise to implement these advanced techniques.
If you ever want to advance to commercial cultivation with a cannabis company, do yourself a favor and learn about it—and put it to use now. You’ll be a more knowledgeable and successful grower as a result! Now that you are understanding water ppm for cannabis it's time to get growing!
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Luis Cordova is a distinguished author, and renowned expert in cannabis cultivation, who possesses a Master's degree in Plant Biotechnology and Pharmaceutical Science. As a valued contributor to highly esteemed publications such as Cannabis Training University and Maximum Yield Magazine, Luis has emerged as a trusted source of guidance and knowledge in the cannabis industry. Having written thousands of informative articles, Luis is widely recognized for his comprehensive expertise on cultivating cannabis, both indoors and outdoors.