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!
PPM & EC
Don't be daunted by these technical-sounding terms. Parts Per Million and Electrical Conductivity are two ways of saying the practically same thing. Now, we could get really technical really fast here in comparing ppm and EC, but for the sake of clarity, let's stick to ppm for the moment.
PPM is a way of measuring the amount of minerals already dissolved in your water, and varies from source to source and place to place. For example, if you have a ppm reading of 100 there are 100 milligrammes per litre of minerals already in your water. Although this is a microscopic amount, the canny cannabis grower knows that plants can only absorb a limited amount of nutrients per day and adjusting for ppm helps get the most from your crops.
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.
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.
If you use tap water, your reading should be between 50 and 300 ppm here in the EU as standard.
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.
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.
GETTING TECHNICAL WITH EC & PPM
Strap your brains in bitches; 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.
EXTRA WATER QUALITY TIPS
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!