Explains how to measure pH and dissolved solids in water, and why these measurements are important for growing marijuana.
The pH level of your water is described in a range from 0-14, with 0 being most acidic, 7 neutral, and 14 most alkaline.
Generally speaking, for good plant growth your pH level should be maintained at 5.6-6.3 for hydro and 5.8-6.5 for soil.
Your plants will not be able to absorb nutrients properly when the pH level is off and they can get sick from deficiencies and experience stunted and slow growth.
The pH level of your water is affected by the nutrients you add to it. pH should be regularly monitored and managed to ensure it stays in the correct zone for optimal growth.
Dissolved solids are usually measured in parts per million (ppm). They are the amounts of minerals in the water – including the fertilizer you add. Water that has very low dissolved solids is soft water. Hard water is the opposite and contains a lot of dissolved solids.
Water that is soft will have dramatic pH swings when acids or alkali are added. Very small amounts of an acidic substance will lower the pH by a lot, and small amounts of an alkali will raise the pH dramatically. If you aren’t paying attention, your could swing pH to levels that are dangerous to plants just by adding a small amount of fertilizer. If your water is too soft, its a good idea to make it harder by adding Cal-Mag or calcium nitrate. Aim for a starting level of 125-425 ppm for your water. This will make the water less susceptible to pH swings.
Hard water can lead to over fertilization problems with specific nutrients when fertilizer is added that contains nutrients that are already present in the hard water. If you are stuck dealing with hard water a way to be sure your solution contains the right levels of nutrients is to use a water testing kit. With a water testing kit you’ll know not only total dissolved solids in the water, but the levels of the individual nutrients also.
The tap water you start with can be either hard or soft depending on where you live. If your tap water has a ppm of 125-425 it would be considered soft to slightly hard, which is a good starting level that is generally compatible with most fertilizer programs.
Measuring individual nutrients with chemical testing kit
Many fertilizer manufacturers will suggest a ppm range for your water when using their products. But how do you know that your solution has the correct levels of the individual nutrients? A water testing kit can give you this additional information. The chart below shows target ppm for the key individual nutrients.
|Nutrient||Vegetative (Grow)||Flowering (Bloom)|
|Nitrogen||200-250 ppm||0-50 ppm|
|Phosphorus||60-80 ppm||100-150 ppm|
|Potassium||250-350 ppm||50-75 ppm|
|Magnesium||50-80 ppm||0 ppm|
To manage your pH and ppm, you need a pH and tds/ppm meter. This tool will show you the total dissolved solids and water pH. For greater precision, a water testing kit that tells you the volume of the individual nutrients is also helpful.
The first thing you should do is make sure the water you are starting with is not too hard or too soft. Aim for a starting ppm of 125-150. To increase the total dissolved solids you can use Cal-Mag or calcium nitrate. To decrease it, you’ll need a reverse osmosis machine or a charcoal / chemical de-ionizer to create soft water that can be mixed in with the hard water to reduce its ppm.
The easiest way to raise or lower pH is to use chemicals called “pH up” and “pH down”. You add drops of these chemicals to the water until the pH is adjusted to the right level.
You can also use the household chemicals in the chart below to adjust pH.
|Use to neutralize acid (raises pH)||Use to lower alkaline (lowers pH)|
|wood ash||kombucha tea|