ppm for seedlings

PPM: What It Is and How To Track It

by Sirius Fourside

If you’ve ever tried to learn how to grow cannabis online or via cannabis growing forums, you’ve probably seen a lot of abbreviations thrown around.

LST, TDS, par, EC, HPS…there are just too many!

One that you’ve probably seen by now is “ppm”.

If you’re like me, you’ve probably avoided learning about this term altogether as it seems to add another layer of complexity to cannabis growing. However, when I finally looked into it, I realized it wasn’t a complex topic at all and it helped me grow better weed.

Today, I will clear up some of the most common questions on the subject, such as “What is ppm?”, what a TDS meter has to do with all this, and some other info so that you will be empowered with new knowledge. The best part is that it’s really simple and there isn’t a lot to it.

Read on for a quick upgrade your growing knowledge!

What IS PPM?

PPM is a unit of measurement, and it’s an initialism for Parts Per Million. This term is used in cannabis cultivation to refer to the concentration of Total Dissolved Solids (TDS) in the water you give your plants. This is a way for growers to refer to exactly how much minerals and other substances are in their water. This information is useful since plants can only intake so many minerals and stuff at a time. This is also useful for DWC growers who need to know the current condition of their reservoir water.

1 part per million is the equivalent of 1mg of solubles per liter of water which is a minuscule amount to measure! Drinking water tested in the US can measure as low as 0ppm (for reverse osmosis, or distilled water) or as high as 700ppm (very poor quality tap water), but most tap water will fall in the 200ppm-400ppm range.

What Is A TDS Meter?

A TDS meter is a tool used to measure ppm. Technically, you measure the TDS of water, and you measure it in ppm. However, most people just skip over TDS and use ppm for both terms.

There are many TDS meters of varying cost and abilities; some also measure temperature or have hold buttons, some measure a higher range of ppm than others.

For those looking into purchasing a TDS meter, know that the range of ppm a particular meter measures shouldn’t be much of a factor for you. Some TDS meters measure up to 5000ppm and some go up to 9999ppm, but for cannabis cultivation, you will rarely see anything above 3500ppm. In fact, in all of the General Hydroponics feeding schedules, the highest ppm is calls for is 1500ppm max. This doesn’t mean you need a meter that only reads up to 1500ppm, but it does mean the ability of a meter to read over 5000ppm probably isn’t needed.

What Is an EC Meter?

EC meters measure the Electrical Conductivity of the water they’re testing. This reading is useful for…measuring the amount of solubles in your water!

So, what’s the difference between a TDS meter and an EC meter?

When it comes to growing cannabis, there isn’t much of a difference at all. In fact, many TDS meters actually measure the electric conductivity of liquids and then convert those results into ppm. In other words, many TDS meters are actually EC meters in disguise!

Electrical conductivity is measured in S/m (Siemens per meter…no giggling!), but since we’re dealing with stuff on such a minuscule scale, readings will show up as μS (micro – one millionth – siemens per meter) or mS/m(milli – one thousandth – siemens per meter).

Although EC meters function just as well if not better than TDS meters, I would recommend against getting one. Most feeding charts or sources of information that talk about water quality will give measurements in ppm. EC meter readings (mS/m) can easily be converted to ppm, but you’ll save yourself some trouble by starting in the right unit of measurement.

It’s not that TDS meters are better than EC meters. In fact, EC meters are a more accurate and consistent way to measure stuff in your water. TDS meters (and ppm as a unit of measurement) are more widely used so it ends up being a more convenient choice.

Do I Really Need to Measure PPMs?

For a large part of my growing career, I ignored using a TDS meter or even learning what they do. Although I don’t recommend that strategy as a way to deal with any of your problems, I can say that I still managed to grow sticky, potent bud despite my resistance to learn about the subject.

In short, I’m confident that anyone can grow a beautiful set of plants from seed to harvest without ever needing to invest in a TDS meter.

However, having a TDS meter can help to prevent or solve problems with nutrient burn and/or overfeeding your plants. If you frequently find that your plants suffer from nutrient burn despite giving them a very small amount of nutrients, you might want to invest the $25 or so to get a TDS meter. Note: If you get a TDS meter, you are definitely going to need calibration solution to make sure the meter is giving you proper readings. I recommend 1000ppm calibration solution which will cost about $10.

How to Measure PPM

This is a really easy process!

  1. Get a TDS meter. I recommend the HM Digital AP-1 as it’s cheap, it has a few handy features(hold button, on-screen temperature), and it doesn’t seem to need recalibration often if at all.
  2. Get calibration solution. This isn’t absolutely necessary, but I would definitely recommend it as sometimes meters come out of the package needing calibration.
  3. Calibrate your TDS meter. Instructions will be on the package; the whole process takes 1 -3 minutes.
  4. Turn on the TDS meter, wait for it to read zero, and insert the electrode into the water you’re testing. If you have a hold button, press it to lock the ppm in. If not, make a note of what the meter reads.

That’s it! You now have the ppm of the water you’re testing. Keep in mind this can be done to several things to give you helpful information:

  • Your tap water
    • Know what’s in your water before you add nutrients to it. Hard water (water with lots of “stuff” in it) can make it so you need very little nutrients before your plants get nutrient burn.
  • Nutrient water
    • Make sure you’re not giving your plants water that will (nutrient) burn them.
  • DWC/Top Fed DWC Reservoirs
    • Make sure the nutrient concentration in your reservoir isn’t spiking as the amount of water goes down. Also, knowing the ppm of your reservoir water makes it easy to grow pristine plants.

What to Do with This Information

Once you have your ppm, you can make proper adjustments to get it in the desirable range. Speaking of which, you’re going to need to know what ppm range you want for your water. This can vary depending on which nutrients you use, but here are some good guidelines:

  • Tap water: 400ppm or below; 400 is high for tap water.
  • Nutrient Water: 400ppm – 800ppm total
  • DWC Reservoir water: 400ppm – 1000ppm

Now that we have our goals, we can make the proper adjustments to get the ppm to where it should be. Here are a few water-related issues you might into and some handy solutions.

Tap water ppm is too high:

  • There are several home options available which can drastically lower the ppm in your tap water. Some of these include carbon filtering, distillation, and reverse osmosis. Reverse osmosis will clean your water so effectively that you’ll need to add calcium/magnesium back into the water.

Adding a normal amount of nutrients makes ppm too high:

  • This means you’re probably using water that had high ppm before the nutrients. Try using nutrients made for “hard water”(water with a high concentration of minerals), such as Flora Micro Hard Water. This will lower the overall ppm.

DWC Reservoir ppm is too high/low:

  • Too high: Add plain ph’d water to the reservoir and test. Repeat until your reservoir reaches a safe fill point, or the ppm is in the correct range. If the ppm is still too high, you can wait for the plant to lower the water levels, or you can change the reservoir water altogether.
  • Too low: Do the same as you would if the ppm were too high, but instead, top-off with nutrient-rich water.

Everything You Need to Find Your PPM

HM Digital AP-1 TDS Meter: Cheap, feature-rich, and powerful! I’ve been using this PPM meter for over 4 years and it still works great.

PPM is a unit of measurement for tracking how much "stuff" is in your water. This is useful for growing cannabis as well as making sure your water is safe!

Cannabis & Water Quality Part 2: PPM & EC

Getting to grips with water quality is a factor that can distinguish between a novice and a veteran hobby cannabis grower. Here is part two of our guide, focusing on PPM and the EC of your water.


Water is a foundation of life. This is no less true for cannabis, which relies on water for a whole array of functions. In our previous blog on water quality, we assessed why water is important, and how pH can affect many aspects of your grow. Today we are going into a bit more detail with ppm and EC. Both are more advanced aspects of cannabis growing that need to be taken into account, and getting your head around it will help push your skills to the max. For the novice, while important, this information is not essential to grow. It is still possible to get great results without it, but it will certainly help!


To understand the nutrient concentration of your soil, you’ll want to test both the pH and PPM or EC of your runoff.


PPM is a measurement that gives you an indication of the amount of nutrients present in your growing medium. This is super important as it guides your next feed and allows you to avoid over- or underfeeding your plants. Measuring PPM is simple and can be done using most pH meters.


EC, or electrical conductivity, is another measurement that helps us determine the amount of nutrients present in the growing medium. The more nutrients in the medium, the higher the EC reading of your runoff. Measuring EC is simple with our DiST 4 Pocket Conductivity Tester by Hanna Instruments. Remember to measure your runoff regularly to know when to feed your plants, and how much to feed them.


For a clear picture of how much nutrients your plants are getting, you need to measure the PPM or EC of both your nutrient solution/reservoir (if you’re using hydroponics) and your runoff. Ideally, the PPM or EC reading of your runoff should always be lower, which shows your plants are taking up nutrients when you feed them. If your PPM/EC readings are super low in your runoff, it’s a sign you need to up your nutrients.

If there is no change in PPM/EC between your nutrients and runoff, this means your plants aren’t taking up nutrients properly. This is usually caused by spikes or drops in pH.

If the PPM/EC reading is higher in your runoff than in your nutrient solution, you’ll likely be dealing with salt buildup around the roots. As you feed your plants, this buildup slowly dissolves back into your runoff, driving up your PPM/EC readings. 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 and can be mixed right into their water. Alternatively, you can also use filtered, pH-neutral water to flush your roots. Just keep in mind that this process takes multiple attempts.

PPM (Hannah) EC (mS/cm2) PPM (Hannah) EC (mS/cm2)
Early Growth 350 – 400 ppm 0,7 – 0,8 400 – 500 ppm 0,8 – 1
Seedling 400 – 500 ppm 1 – 1,2 500 – 600 ppm 1 – 1,3
Transition 550 – 650 ppm 1,3 – 1,5 600 – 750 ppm 1,2 – 1,5
Vegetative Stage 650 – 750 ppm 1,6 – 1,7 800 – 850 ppm 1,6 – 1,7
Vegetative Stage 750 – 800 ppm 1,7 – 1,8 850 – 900 ppm 1,7 – 1,8
Vegetative Stage 850 – 900 ppm 1,8 – 1,9 900 – 950 ppm 1,8 – 1,9
Flowering Stage 900 – 950 ppm 1,9 – 2 950 – 1000 ppm 1,9 – 2
Flowering Stage 950 – 1050 ppm 2 – 2,2 1000 – 1050 ppm 2 – 2,1
Flowering Stage 1050 – 1100 ppm 2,2 – 2,3 1050 – 1100 ppm 2,1 – 2,2
Flowering Stage 1100 – 1150 ppm 2,3 – 2,4 1100 – 1150 ppm 2,2 – 2,3
Flushing 0 – 400 ppm 0 – 0,8 0 – 400 ppm 0 – 0,8
PPM (Hannah) EC (mS/cm2)
Early Growth 350 – 400 ppm 0,7 – 0,8
Seedling 400 – 500 ppm 1 – 1,2
Transition 550 – 650 ppm 1,3 – 1,5
Vegetative Stage 650 – 750 ppm 1,6 – 1,7
Vegetative Stage 750 – 800 ppm 1,7 – 1,8
Vegetative Stage 850 – 900 ppm 1,8 – 1,9
Flowering Stage 900 – 950 ppm 1,9 – 2
Flowering Stage 950 – 1050 ppm 2 – 2,2
Flowering Stage 1050 – 1100 ppm 2,2 – 2,3
Flowering Stage 1100 – 1150 ppm 2,3 – 2,4
Flushing 0 – 400 ppm 0 – 0,8
PPM (Hannah) EC (mS/cm2)
Early Growth 400 – 500 ppm 0,8 – 1
Seedling 500 – 600 ppm 1 – 1,3
Transition 600 – 750 ppm 1,2 – 1,5
Vegetative Stage 800 – 850 ppm 1,6 – 1,7
Vegetative Stage 850 – 900 ppm 1,7 – 1,8
Vegetative Stage 900 – 950 ppm 1,8 – 1,9
Flowering Stage 950 – 1000 ppm 1,9 – 2
Flowering Stage 1000 – 1050 ppm 2 – 2,1
Flowering Stage 1050 – 1100 ppm 2,1 – 2,2
Flowering Stage 1100 – 1150 ppm 2,2 – 2,3
Flushing 0 – 400 ppm 0 – 0,8


Knowing your PPM helps you avoid possible burning by letting you know when to adjust the amount of nutrient minerals you add to your water. Cannabis enjoys 500-600 ppm after cloning, 800-900 ppm when vegetating, and 1000-1100 ppm when flowering. So knowing the mineral content of your water before mixing your nutes can avoid stressing you and your plants. For DWC (hydroponic) growers, it is important to know the condition of the reservoir water, as minerals can deplete as the water level drops – it is a heads-up for you to just top things up as required.

There are many probes, devices and metres on the market all able to measure ppm. The most common is a TDS metre (total dissolved solids). What you go for really depends on your budget, and desire to get technical and nerdy with your grow. Most have a range of 3500, which is all you will ever need for cannabis, but if you like the overkill some will read up to 9999.

1. Once you have calibrated your TDS metre, turn it on, make sure it is reading zero and put it in the water you want to test – hey presto, there’s your ppm reading. If you are using reverse osmosis water, the reading will be 0 to 10 ppm as it is completely free of minerals.

2. If you use tap water, your reading should be between 50 and 300 ppm here in the EU as standard.

3. If your town’s plumbing is old, or you are using well water from limestone strata, you may get a reading of up to 500 to 700ppm because of the mineral build up.

4. If your water is reading over 500 ppm, you need to do something about it, as it will compete with and lock out the nutrients you actually want your cannabis to uptake. Either you need to get some nutes designed to be used in hard-water areas, or you need to treat your water at home, either through carbon filters, distillation, or reverse osmosis.

Conductivity Tester


This is where things get technical.

EC, or Electrical Conductivity, is a measure of the salinity of a water sample.

The theory being that saline water is charged with sodium ions and this charge can be measured by an EC metre, which tells you the conductivity of your water sample – in microsiemens per centimetre. EC works by assuming an ionic conductivity of sodium as .51 microsiemens per centimetre. This is the base charge off which metres calculate conductivity.

If your water is too saline, it can affect your plants in two ways. It can increase the toxicity of sodium at the root ball and increase osmotic pressure at the roots inhibiting nutrient uptake.

PPM measures the overall mineral content of your water, regardless of what those minerals are.

Accurate ppm readings are obtained by gently evaporating the water sample and analysing the remaining residue. Other than sodium chloride most other minerals are hardly present in nearly all naturally occurring water and are not of any real worry. These minerals are usually trace amounts of calcium carbonate, magnesium and micro traces of several other elements.

If you approach your local water authority, they can usually supply you with a mineral analysis of your local water supply.

There are conversions for microsiemens per centimetre to parts per million and back again but most metres do these conversions for you.

Organic soil and outdoor growers have an advantage again when it comes to ppm and EC. The microorganisms provide a buffer that helps protect the plant from fluctuations in ppm or EC and there is a greater margin for error when watering.

Never be complacent, though. Always check your water quality, even from rivers and creeks. You never know what could be washed in upstream during rain that could make your water toxic.


• Who thinks rain water is neutral? It is a common misconception and is actually mildly acidic. Carbon dioxide dissolves in rain and makes it into a very mild carbolic acid with a pH of about 5.6. Don’t worry, though, once it has sat for a while in a tank or dam or reservoir it releases the carbon dioxide and balances out at 7. Ever noticed how plants grow like mad after rain? That’s why.

• When you put your water through a reverse osmosis filter, it makes your water completely mineral free. Never use this water unmodified to flush your plants or as a foliage spray. RO water will strip nutrients from your plants, especially calcium and magnesium. Label your bottles clearly.

• Put aerators on your faucets. If filling a container with a hose, make the water froth and bubble to enliven and oxygenate.

• In cold climates try and keep your water at 25°C.

There you have it! Things get quite technical, so don’t worry if it takes a while to pick up. Actively working to ensure you have the best water quality you can will help minimise any potential growing problems, as well as give your cannabis what it needs to thrive. The more you know!

Part. 1: pH Good quality water is a foundation of a great cannabis grow.

Part. 3: Choosing A Water Source Choosing a water source is a crucial decision when it comes to growing marijuana.

Water quality is an essential consideration when it comes to advanced cannabis growing. In part two of out guide, we look at PPM and EC.