Whether you are growing in soil or hydroponically, the quality of the water you use is an important factor to consider, as it has a major impact on plant growth and the quality of the nutrient solution (water, food and possibly additives).
Depending on the amount of bi-carbonates in it, water is described as being either ‘hard’ (high levels of bi-carbonates) or soft’ (low levels), and measured on a scale known as pH (potential of hydrogen).
PH
PH is a measurement of how acidic or alkaline the water/nutrient solution is, and runs on a scale of 1 to 14 with neutral (pure water) being 7. The pH level affects the availability of nutrients within the water/solution, and therefore how easily the plants can access these nutrients (feed). PH is the most important factor to be controlled with water/nutrient solutions and poor pH management can produce weak plants with minimal yields, this is more the case with hydroponics than soil growing.
Cannabis prefers a slightly acidic level of around pH 6 (in a range of pH 5.6 – 6.4). It is only around this level that there is significant availability of all the nutrients required. High pH levels can reduce the availability of iron, manganese, boron, copper, zinc and phosphorus whereas low pH levels effect the availability of potassium, sulphur, calcium, magnesium and phosphorus.
It should be noted that the pH scale is logarithmic. This means that every point on the scale represents a tenfold increase in either acidity or alkalinity. This is why a small change in the pH level can have such a major impact on the nutrient availability in the solution.
PH 7 = NEUTRAL (PURE WATER).
PH 6 = 10 TIMES AS ACIDIC AS PH 7.
PH 5 = 100 TIMES AS ACIDIC AS PH 7.
PH 4 = 1,000 TIMES AS ACIDIC AS PH 7.
Etc.
With re-circulating hydroponic systems there are many factors which can effect the pH of the nutrient solution, so daily checking and adjusting is required with renewal every one or two weeks.
MEASURING PH
The pH level of your nutrient solution can be checked in two ways:
LIQUID PH TEST KIT
This is a simple way to measure the pH level and test kits and can be purchased for about £4. A re-agent is added to a sample of the water/solution which changes colour according to the pH level. This is then compared to a colour card to give the pH. Although this may seem a bit crude, it is accurate enough and many professional gardeners use this method, as pH meters are delicate instruments that require care and constant re-calibration. Different pH test kits cover different ranges, for cultivation the narrow range kits are used where the re-agent covers pH 6.0 – 7.6, which are far more accurate than the wider range kits.
HOW TO USE A LIQUID PH TEST KIT
Take a measured sample (usually just one or two mls) of the water/nutrient solution. Add a measured amount (usually one or two drops) of the pH reagent.
The sample will then change colour (somewhere between orange and blue), by comparing this to a sample card (or test strip) the pH level can be judged.
It’s as easy as that.
PH METER
Electronic pH meters give a numerical digital reading of the pH level, so are accurate and easy to use. They are very sensitive volt meters which measure the pressure of the electricity in the solution, which is affected by acidity/alkalinity. Unlike standard volt meters they have sophisticated amplifiers which increase the power of the probe, as the amounts of electricity being measured are so small. A solution will give different pH readings at different temperatures, but good pH meters will compensate for any differences. Ph meters are very sensitive pieces of equipment and require a lot of care and maintenance, especially in hard water areas, and some will need calibrating on a regular basis. Meters are calibrated using pH buffers, these are simple solutions of a known pH, against which the meter can be checked.
PH TEST STRIPS
PH test strips and water hardness strips are also available but are not as accurate as the liquid pH test kits.
CORRECTING THE PH LEVEL
If the water/nutrient solution is not be at the ideal level of pH 6 you will need to correct it. This is easily done by adding a ‘pH solution’. ‘PH up’ (usually potassium or calcium hydroxide) will make the solution more alkaline and will raise the pH level, ‘pH down’ (usually phosphoric or nitric acid) will make the solution more acidic and will lower the pH level. You will only need to use a few drops of pH solution per litre, depending on the quality of the water. It is best to check and adjust the pH level after adding any nutrient concentrates or additives, so
Get a measured amount of water.
Add any food or additives.
Check the pH level.
Add Ph solution (‘up’ or ‘down’).
Check the pH level again.
Possibly repeat steps 4 + 5 until correct (pH 6)
WATER QUALITY
There are two main sources for water:
RAINWATER
Plants have developed over millions of years to feed from rainwater, so this is the best type of water to use. It is the purest form of water (with few or no dissolved salts) and therefore has a low pH level, however it can be difficult to collect sufficient rainwater to maintain a hydroponic system. If you can use rainwater then hold it in a covered tank and filter out any bits, also make sure that the nutrient concentrate you purchase is suitable for rainwater.
Rainwater is particularly recommended for soil growers in areas where the tap water is above pH 7.5/8.0 as a large build-up of salts can occur within the growing medium, even if you are correcting the pH levels. These elements in tap water are not required by the plant so every time it is watered more salts are added, in time these will build up and cause problems with salinity. This is not such a problem with hydroponics as the nutrient solution is removed and replaced on a regular basis.
TAP WATER
The main problem with tap water is that it contains high levels of un-dissolved salts (particularly sodium chloride) which increase the pH level. Most of the U.K. (70%) has hard water (with pH levels above pH 7.5, too high for plants) so you will need to bring down the pH level of your water/nutrient solution (to 6.0). Soft water areas have a low pH, so you will need to raise the pH level. Some manufacturers adapt their nutrient concentrates specifically for hard and soft water areas, but you will still have to check and correct the pH level. Tap water should also be left to sit for a day to let the added chlorine evaporate off and to settle to room temperature
Depending on the amount of bi-carbonates in it, water is described as being either ‘hard’ (high levels of bi-carbonates) or soft’ (low levels), and measured on a scale known as pH (potential of hydrogen).
PH
PH is a measurement of how acidic or alkaline the water/nutrient solution is, and runs on a scale of 1 to 14 with neutral (pure water) being 7. The pH level affects the availability of nutrients within the water/solution, and therefore how easily the plants can access these nutrients (feed). PH is the most important factor to be controlled with water/nutrient solutions and poor pH management can produce weak plants with minimal yields, this is more the case with hydroponics than soil growing.
Cannabis prefers a slightly acidic level of around pH 6 (in a range of pH 5.6 – 6.4). It is only around this level that there is significant availability of all the nutrients required. High pH levels can reduce the availability of iron, manganese, boron, copper, zinc and phosphorus whereas low pH levels effect the availability of potassium, sulphur, calcium, magnesium and phosphorus.
It should be noted that the pH scale is logarithmic. This means that every point on the scale represents a tenfold increase in either acidity or alkalinity. This is why a small change in the pH level can have such a major impact on the nutrient availability in the solution.
PH 7 = NEUTRAL (PURE WATER).
PH 6 = 10 TIMES AS ACIDIC AS PH 7.
PH 5 = 100 TIMES AS ACIDIC AS PH 7.
PH 4 = 1,000 TIMES AS ACIDIC AS PH 7.
Etc.
With re-circulating hydroponic systems there are many factors which can effect the pH of the nutrient solution, so daily checking and adjusting is required with renewal every one or two weeks.
MEASURING PH
The pH level of your nutrient solution can be checked in two ways:
LIQUID PH TEST KIT
This is a simple way to measure the pH level and test kits and can be purchased for about £4. A re-agent is added to a sample of the water/solution which changes colour according to the pH level. This is then compared to a colour card to give the pH. Although this may seem a bit crude, it is accurate enough and many professional gardeners use this method, as pH meters are delicate instruments that require care and constant re-calibration. Different pH test kits cover different ranges, for cultivation the narrow range kits are used where the re-agent covers pH 6.0 – 7.6, which are far more accurate than the wider range kits.
HOW TO USE A LIQUID PH TEST KIT
Take a measured sample (usually just one or two mls) of the water/nutrient solution. Add a measured amount (usually one or two drops) of the pH reagent.
The sample will then change colour (somewhere between orange and blue), by comparing this to a sample card (or test strip) the pH level can be judged.
It’s as easy as that.
PH METER
Electronic pH meters give a numerical digital reading of the pH level, so are accurate and easy to use. They are very sensitive volt meters which measure the pressure of the electricity in the solution, which is affected by acidity/alkalinity. Unlike standard volt meters they have sophisticated amplifiers which increase the power of the probe, as the amounts of electricity being measured are so small. A solution will give different pH readings at different temperatures, but good pH meters will compensate for any differences. Ph meters are very sensitive pieces of equipment and require a lot of care and maintenance, especially in hard water areas, and some will need calibrating on a regular basis. Meters are calibrated using pH buffers, these are simple solutions of a known pH, against which the meter can be checked.
PH TEST STRIPS
PH test strips and water hardness strips are also available but are not as accurate as the liquid pH test kits.
CORRECTING THE PH LEVEL
If the water/nutrient solution is not be at the ideal level of pH 6 you will need to correct it. This is easily done by adding a ‘pH solution’. ‘PH up’ (usually potassium or calcium hydroxide) will make the solution more alkaline and will raise the pH level, ‘pH down’ (usually phosphoric or nitric acid) will make the solution more acidic and will lower the pH level. You will only need to use a few drops of pH solution per litre, depending on the quality of the water. It is best to check and adjust the pH level after adding any nutrient concentrates or additives, so
Get a measured amount of water.
Add any food or additives.
Check the pH level.
Add Ph solution (‘up’ or ‘down’).
Check the pH level again.
Possibly repeat steps 4 + 5 until correct (pH 6)
WATER QUALITY
There are two main sources for water:
RAINWATER
Plants have developed over millions of years to feed from rainwater, so this is the best type of water to use. It is the purest form of water (with few or no dissolved salts) and therefore has a low pH level, however it can be difficult to collect sufficient rainwater to maintain a hydroponic system. If you can use rainwater then hold it in a covered tank and filter out any bits, also make sure that the nutrient concentrate you purchase is suitable for rainwater.
Rainwater is particularly recommended for soil growers in areas where the tap water is above pH 7.5/8.0 as a large build-up of salts can occur within the growing medium, even if you are correcting the pH levels. These elements in tap water are not required by the plant so every time it is watered more salts are added, in time these will build up and cause problems with salinity. This is not such a problem with hydroponics as the nutrient solution is removed and replaced on a regular basis.
TAP WATER
The main problem with tap water is that it contains high levels of un-dissolved salts (particularly sodium chloride) which increase the pH level. Most of the U.K. (70%) has hard water (with pH levels above pH 7.5, too high for plants) so you will need to bring down the pH level of your water/nutrient solution (to 6.0). Soft water areas have a low pH, so you will need to raise the pH level. Some manufacturers adapt their nutrient concentrates specifically for hard and soft water areas, but you will still have to check and correct the pH level. Tap water should also be left to sit for a day to let the added chlorine evaporate off and to settle to room temperature
