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!
- 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.
- Get calibration solution. This isn’t absolutely necessary, but I would definitely recommend it as sometimes meters come out of the package needing calibration.
- Calibrate your TDS meter. Instructions will be on the package; the whole process takes 1 -3 minutes.
- 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!