Nutrients – EC and PPM Testing Basics

what does 'ec' mean?

EC stands for Electrical Conductivity and this measurement can help us to see the amount of nutrients in our solution. A higher EC reading will mean the higher the level of nutrients in your water. We measure EC as S/m (siemens per metre). 

what does 'ppm' mean?

PPM stands for Parts Per Million. You can use this reading to determine the concentration of TDS (Total Dissolved Solids) in your water. 1 part per million is the equal to 1mg of soluble per litre of water. Like an EC reading, it can also tell you the level of nutrients and other substances there are in the water. This can be useful to know as your cannabis plant will only be able to absorb a certain amount of nutrients at one time. By looking at these readings, the grower can determine whether to add more nutrients to the water or not.

At first all these terms can seem confusing for beginner growers and really, you can still grow a potent plant without knowing about testing the EC or PPM. However, by learning this stuff, it will definitely help you in the long run and can help to produce higher quality plants and buds. 

Read the testing chart at the bottom of the page for detailed information on optimal readings. 

purple cannabis flowers

measuring the ec of your water

An EC meter will measure the electrical conductivity of your water. The higher the reading, the more soluble there are in your water. EC is tested by S/m (siemens per metre) but you will usually find the reading to also be measured as mS/m(milli to one thousandth siemens per metre), as the readings are on such a small scale, they are minute.

An EC meter can be an accurate way of measuring the nutrient level and other solubles in the water, but a TDS metre will also take an EC reading, and then convert that into PPM. You can still convert the reading of your EC meter yourself, but to save time and effort it may be easier to buy a TDS meter, as most cannabis feeding schedules will measure in PPM.

For those who like measuring in EC, the reading should be around 0.8 to 1.0 during the initial vegetative stage and between 1.2 to 2 during the flowering stage. Adding more water will lower an EC reading if it is too high and adding more nutrients will help an EC reading that is too low.

Note that EC readings will change according to the temperature at the time they are taken. Generally, they will change about 2.5% per degree Celsius. 

ph, ec and tds meter

measuring the ppm of your water

The PPM of your water is measured by using a TDS meter. You will get a TDS reading, which is then measured using PPM. Many growers use these two terms interchangeably.

When buying a TDS meter, you will see a range of PPM levels, some can take a reading up to 9999PPM. For cannabis growing, you normally will not need one that goes to that level, as most feeding schedules will require the level to go no higher than around 1500PPM. The best TDS levels for cannabis are around 750ppm to 1500ppm, depending on where the plant is on the growth cycle, and the size of the plant/ plus how much nutrients it can absorb.

Using a TDS meter, you can easily check how nutrient rich your water solution is and if there are too many or too little nutrients in the water. This can help to control nutrient burn or nutrient deficiencies in your plant. 

how to use a tds meter

Before measuring the PPM, it is a good idea to buy a calibration solution to ensure accurate readings from your TDS meter. These can be bought pretty cheap (a 1000ppm calibration solution is a good choice). If you are on a budget, you can still use the metre without this so do not worry.

Calibrating the TDS metre is very easily done by following the instructions on the package and will only take a few minutes of your time.

After turning on the TDS meter and waiting for it to read zero, put the electrode into the water. It should show you a reading. If you have a hold button, press this and it will lock in the PPM. And that is how quick it is. You can use this to test your tap water, nutrient solution, and water in your reservoir.

If your tap water is quite hard, then you may not need to add a lot of nutrients to it, as this could cause nutrient burn in your cannabis plant. Testing your reservoir water in hydroponic systems is a good idea, as this could change over time. Keeping a regular check on the EC, PPM and also the pH readings will help your plants to grow optimally and produce quality buds and flowers. 

close up cannabis flowers

know the correct readings

Knowing what the correct PPM or EC readings are will help you to determine if you need to make changes to your nutrient solution. Here are some optimal readings for PPM:

  • Nutrient water: 400ppm to 800ppm
  • Reservoir water: 400ppm to 1000ppm
  • Tap water: 400ppm or below (average tap water is around 200 to 400ppm)

If you find that adding the required amount of nutrients to your tap water is still resulting in nutrient burn, it is possible the tap water had a high PPM level to begin with. This can happen if your tap water is quite ‘hard’, meaning there is a higher concentration of minerals and other solutions in it. Using nutrients designed for hard water can help to reduce the PPM reading.

To reduce the PPM level in your tap water before hand, you can try a carbon filter, distillation, or reverse osmosis which will thoroughly clean your water (calcium/magnesium may need to be added back in the water after this process). 

hydro and soil ec and ppm chart