Whats is PPM and how to measure it?

Just like human beings, cannabis plants will become what they consume. To keep your plants healthy, you need to exactly know what they are consuming and adjust that to their needs. Think about things like nutrients, the right PH levels and what kind of stuff is in your soil. Another important thing you need to think about is your water source and what it consist of. That’s why you should test the PPM of your water before mixing it with nutrients or giving it to your plants.

In this article I am going to explain what PPM exactly is, how to measure it and what do when it’s levels are too high! The first impression of PPM most people have is that it’s complicated and more suitable for experiences growers to work with. However this is not true as you will see after reading this.

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What exactly is PPM (parts per million)? 

If you want to know how much the PPM in your water is, you actually are looking for the “hardness” of your water. Simply said, PPM (parts per million) is a measuring unit that tells you how many minerals, metals and other substances are in that particulair water. So when talking about PPM, growers are refering to the concentration of Total dissolved solids (TDS) that are in the water they are giving their plants.

1 PPM is actually a very small amount to measure and is actually the same as 1MG of solubles per litre water. To give you an idea of these levels we’re going to take a look at tapwater:

Drinking water in the U.S can be very different depending on the area you are in. Some areas/stores offer very clean water as low as 0PPM (distilled water). However some area’s have tapwater that is measured up to 700PPM. (very low quality, contains lot’s of other substances). Most tapwater around the western world is measured between 200-400PPM.

Why is this important for growers?

Measuring the PPM is very important for cannabis growers because a plant is only able to consume a certain amount of minerals at 1 time. So when your water is already full of un-necessery minerals and metals, it’s hard for a plant to get the minerals/nutrients it really needs. This will eventually lead to nutrient deficiencies and ruined plants.

How do I measure the PPM of my water?

Measuring the PPM of your water is quite easy once you know how and have the right equipment (EC/TDS meter). Before you start measuring, you need to know what ppm levels are alright for your plant and which water you need to measure. Your tap water will show different results once it got mixed with nutrients as there are more “parts” or minerals added to it.

First, you need to measure the tapwater without any mixed nutrients. After that you can figure out how much nutrients you can add to the water before it’s PPM gets too high for your plant. “Hard” tap water (high PPM) means less nutrients you can add before it reaches the maximum PPM.

Make sure you use these levels as an indicator: 

  • Tap water: 400PPM or lower, 400 is already quite high!
  • Nutrient water: 400PPM-800PPM (after adding nutrients, try not to go higher then 800PPM)

For example: If your tap water reaches a ppm of 287, you’d be able to add nutrients untill you reach water with a ppm of 400-800 (Around +-650). If you keep the ppm between these level you’ll avoid something we call nutrient burn or overfeeding the plant.

Measuring equipment:

To measure all these levels you could use 2 different meters that are both not expensive and easy to buy online:

  • TDS meter

TDS stands for “Totally dissolved solids” which means all (non-)organic that are dissolved in a liquid. A TDS meter is a very simple meter (similar as PH meter) that will show you directly the results in PPM by holding the senors in water for a while. There are more varieties of TDS meters, some also measure temperature but thats not required for cannabis cultivation.

If you are planning to buy one of these, you need to know that these meters comes in different ranges of PPM. Some meters measure up to 9999PPM, other do not go further then 5000PPM. When growing cannabis, you don’t have to pay much attention to these high ranges. If you take a look at most (Hydrophonics) feeding schedules, you won’t see higher PPM’s then +- 1500 max. We’ll recommend to get one that is able to measure up to 5000PPM, to be sure!

Our recommended TDS-meter!

  • EC meter

EC meters are another way to eventually measure the PPM in the water. An EC meter measures the electrical conductivity of the water. This will show you the amount of solubles in the water. Electrical condictivity will be measured in s/m (Siemens per meter). However because we are dealing with very small stuff, wel will measure it in μS (micro – one millionth – siemens per meter) or mS/m (milli – one thousandth – siemens per meter to be precisely).

So if it basically does the same thing, what’s really the difference between an EC and TDS meter? 

Well in fact there aren’t really many differences between these 2 meters. Lots of times an TDS meter is actually an EC meter that converts it’s electric conductivity results tot PPM instead of showing it in mS/m (So a EC meter disguised as TDS meter). Eventually they give the same result as they show you the harshness of the water, but in a different way.

The main difference is that they measure 2 different things (All disolved solids VS electrical conductivity) and show the results in different measure units (PPM Vs mS/m) which can be easily converted to each other.

Generally a EC meter is a bit more precisely then the TDS meter but we still recommend to get the TDS simply because it takes way less effort. Most information on the web about water quality will talk about PPM so when using a EC meter, you will need to convert the results you get from mS/m to PPM. To save yourself the time and effort you could better go for a TDS meter and directly read the results in PPM.

Our recommended EC-meter!

Start measuring and processing the info

Calibration liquid

Alright, let’s say you got a new TDS meter and want to start testing your water. There is a big chance your meter is not set-up right and needs to be calibrated when it comes out of the package. Thats why we always recommend to get some Calibration liquid with your meter just to be sure (sometimes your meter is fine and this is not required).

The instructions on how to calibrate your meter will be on the package of the liquid. This proces is very easy and will take just a few minutes. Once this is done, you are ready to start measuring:

  • Turn on your meter and wait for it to show 0 (zero)
  • Now only put the electrode in the water you want to test
  • Hold the lock-button to lock the PPM level (or just write it down if you haven’t a lock button)
  • Now you done and you know the PPM of your water

342 PPM calibration solution- For low PPM measuring

1000PPM calibiration solution- For high PPM measuring

What to do next?

Now you know how to measure properly, it’s time to find out what to do with the information you just got. First of all you need to know what PPM levels you should be aiming at. Like told above, tapwater should never contain more then 400PPM. (the lower the better)

As you add nutrients to your tap water, the PPM will increase even more (because you add more minerals to the water). Make sure that nutrient mixed water never passes 800PPM. If one of these waters don’t show the desired PPM levels you have adjust them and lower the PPM in your water:

There are 2 different scenarios you could face when PPM levels aren’t on track:

  • The PPM of your tap water is too high

If this is the case, you have pretty harsh water that is not suitable to give your plants. As you add some nutrients the PPM will increase even more making it hard for the plant to consume the right nutrients which could lead to nutrient burn or deficiencies. Luckily there are options to lower the PPM: Distillation, carbon filtering and reverse osmose are the most used methods (keep in mind the reverse osmose cleans the water so good, you have to add magnesium/calcium afterwards)

  • The PPM of your nutrient mixed water is too high

If your “nutrient mixed” water contains a too high PPM level, there could be 2 things that cause it: The first one is the amount of nutrients. Make sure you won’t add more nutrients then adviced on the package/bottle. When adding nutrients, you are adding minerals and other solubles which massively increase the PPM in water.

The second cause of this problem is simply using tapwater with a too high PPM in the first place. If the tapwater is too harsh (400ppm or higher) and you add nutrients to that it will quickly overpass the 800PPM level. This will definitly cause problems!

As you can see it all begins with the right tap water. Good tap water+ the right amount of nutrients is all you need to make your water suitable for your cannabis plants! 

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