woody
Cultivators Club
Found this article online and thought it was worth a share, @Grey Bear all this info seem ok to you?
Active hydroponic systems based on the principles of Flood and Drain, Nutrient Film Technique (NFT), Deep Water Culture (DWC/Bubbler) and Drip Irrigation are all only as good as the feeds you put into them – so it really does pay to master the art of mixing your water and nutrients together. To give plants unlimited access to the key elements they require for growth, the hydroponic nutrient solution must be within the correct pH range and have a suitable nutrient strength, measured by the electrical conductivity. Fear not though, this is relatively easy to achieve! In our article we discuss both pH and conductivity to find out why they are so important.
Nutrient Solution pH
The pH is the measure of the acidity or alkalinity of a nutrient solution. A pH value of 0 to 6.9 indicates an acidic nutrient solution, 7.1 to 14.0 can be considered more alkaline and a reading of 7 qualifies as neutral. Ideally, the pH range for hydroponics should register between 5.5 and 6.5. If you allow the pH level to fall outside of this range, it will affect your plants’ ability to utilise those nutrients.
Why do I need to bother with pH?
From the chart above you can see that specific elements become more and less available to plants as pH changes. If your pH is out of range and one or more of the key elements are suddenly made unavailable, this will result in poor yields, slow growth rates and nutrient deficiencies.
How do I check my pH?
When you’re in the process of producing a fresh reservoir of nutrient solution, always introduce the additives first, then nutrients and lastly check and adjust the pH.
Reading the pH can be done with a liquid pH test kit or a digital meter.
The liquid pH test kit is fine if you find yourself on a budget – simply take a sample of the solution in the test tube, add a few drops of reagent and give it a shake, then match the colour of the solution against a reference chart.
A digital meter will provide a much more accurate level of control with less messing about – all you do is switch it on and dip the probe into the nutrient solution. If the pH shows as out of range, simply use pH down or pH up.
Top Tips:
- When making up a fresh batch of nutrient solution we recommend setting the pH to 6.0. This allows the nutrient concentration to increase or decrease slightly in an active hydroponic system and still be within range.
- If you have very hard water, we suggest using Nitric Acid pH Down or a combination of this and standard pH Down (phosphoric acid). Nitric acid is very aggressive and better at buffering carbonates in tap water.
- The very alkaline Shogun Silicon can be used in small amounts instead of pH Up.
Silicon is a good example of an additive that you should mix with water only and then add the nutrients. Doing it the other way around results in the high pH of the Silicon reacting with the low pH of the nutrients, which causes clouding of the nutrient solution to occur. This clouding effect is nutrients precipitating out of the solution, consequently becoming unavailable to your plants.
How do I manage my nutrient solution pH?
In active hydroponic systems the nutrient solution can be run to waste or re-circulated. Generally, run to waste is only suitable for drip irrigation and requires minimal pH management – after all as soon as you have set the pH of a new reservoir of nutrient solution it will stay the same until plants begin to drink. Most hydroponic systems re-circulate the solution and require frequent pH check and adjustments. This is due to the plants in the system actively taking up nutrients and water, which alters the pH of the solution returning to the reservoir.
How often should I check the pH?
For an active hydroponic system you should check your pH as and when you can – but the exact frequency depends on the type of system. You will find that a large volume of water in a reservoir will need less pH adjustments than a smaller volume of water. With this in mind you are able to save yourself from having to regularly adjust the pH by always keeping the reservoir as full as possible. Greater amounts of nutrient solution means the pH will take longer to change.
Tip – if you get the chance to choose the size of reservoir for your active hydroponic system, always pick the largest suitable option to ensure that the pH and conductivity drifts off target slowly.
How often should I adjust the pH?
As the pH approaches its upper parameters (6.5 maximum) you should adjust it back. It is good to allow the pH to drift up and down, as this allows the plant to access different quantities of nutrients at different set points. Setting the pH at 5.8 and allowing it to drift up to 6.6 can often provide better results than constant maintenance at 5.8.
Nutrient Solution Conductivity
Nutrient solution strength plays an important role in maintaining the health of a plant. If the nutrient solution is too strong, the leaves of the plant sometimes become leathery, curl downwards or even burn at the tips. Alternatively, a lower than desired concentration of nutrients will see the plant turn yellow, stretch and become susceptible to disease. The strength of a nutrient solution can be detected using a simple device called a conductivity meter. This indirectly measures the amount of dissolved minerals in the solution – with the more nutrient there is in the water, the higher the resulting conductivity reading.
What’s the difference between CF, EC and PPM?
The electrical conductivity of the nutrient solution is read by a meter and converted into units of measure, the most common values used in Hydroponics being Conductivity Factor (CF), Electrical Conductivity (EC) or Parts Per Million (PPM).
In the UK and Europe, CF and EC are most common, whereas in North America PPM appears more often. The problem with PPM is that there are different scales of conversion depending on the meter – 500 (also called TDS) and 700 – so you absolutely must know which one you’re measuring in! The difference between EC and CF is simply the decimal point (e.g. an EC of 1.0 is a CF of 10). The following chart shows the simple relationship between these values.
What is the ideal conductivity?
As your plants grow, their demand for nutrients will change. Generally, young plants like a weaker nutrient solution and mature plants like a stronger nutrient solution. Therefore, as your plants develop gradually increase the conductivity.
The chart above is a general guide on the typical vales you would expect to be using at different growth stages. However, some active hydroponic growing systems require a lower conductivity than others, and environmental factors need consideration too. Read on to find out more…
Why do I need to check the conductivity?
Much like with pH, as the plants in active hydroponic systems take up water and use the nutrients, this will alter the conductivity. How much and in what direction it changes depends on the plant and the growing environment. Hungry plants tend to cause the conductivity to drop, whereas thirsty plants cause the conductivity to go up. In ideal conditions and at the right nutrient strength, as the nutrient solution is used by the plant, the conductivity remains the same.
My conductivity is increasing?!?
If your conductivity is increasing, it means the plant is using more water than nutrients. This often comes down to the grow room being too hot and/or having a low relative humidity, so by correcting these environmental problems you can stop conductivity from rising. If you are unable to reduce your temperature or increase your humidity, try keeping your conductivity lower than usual to allow for upward drift and ensure your reservoir remains topped up as much as possible.
My conductivity is decreasing?!?
If your conductivity is decreasing, it shows that the plant is taking up the nutrients from the solution so you need to increase the nutrient strength. This often happens in ideal environmental conditions where there are no excessive external demands on the plant.
Top Tips for Managing and Measuring Conductivity:
- Measure the conductivity of your tap water – this will give you a good indication of your water hardness. A CF of 0-3 is soft water, 4-5 is moderately hard, and 6 and above is considered hard.
- For optimum conductivity control, use a Reverse Osmosis filter to remove all your tap water contaminant – you’ll then be able to start with a conductivity of zero.
- Active Hydroponic Systems that saturate the root zone with oxygen, such as DWC/Bubblers, require a lower conductivity than media based systems such as drip irrigation or flood and drain. This is due the efficiency at which the plants feed in DWC systems, in fact, the conductivity requirements can be as much as 25% lower than other active hydroponic systems.
Active hydroponic systems based on the principles of Flood and Drain, Nutrient Film Technique (NFT), Deep Water Culture (DWC/Bubbler) and Drip Irrigation are all only as good as the feeds you put into them – so it really does pay to master the art of mixing your water and nutrients together. To give plants unlimited access to the key elements they require for growth, the hydroponic nutrient solution must be within the correct pH range and have a suitable nutrient strength, measured by the electrical conductivity. Fear not though, this is relatively easy to achieve! In our article we discuss both pH and conductivity to find out why they are so important.
Nutrient Solution pH
The pH is the measure of the acidity or alkalinity of a nutrient solution. A pH value of 0 to 6.9 indicates an acidic nutrient solution, 7.1 to 14.0 can be considered more alkaline and a reading of 7 qualifies as neutral. Ideally, the pH range for hydroponics should register between 5.5 and 6.5. If you allow the pH level to fall outside of this range, it will affect your plants’ ability to utilise those nutrients.
From the chart above you can see that specific elements become more and less available to plants as pH changes. If your pH is out of range and one or more of the key elements are suddenly made unavailable, this will result in poor yields, slow growth rates and nutrient deficiencies.
How do I check my pH?
When you’re in the process of producing a fresh reservoir of nutrient solution, always introduce the additives first, then nutrients and lastly check and adjust the pH.
Reading the pH can be done with a liquid pH test kit or a digital meter.
- When making up a fresh batch of nutrient solution we recommend setting the pH to 6.0. This allows the nutrient concentration to increase or decrease slightly in an active hydroponic system and still be within range.
- If you have very hard water, we suggest using Nitric Acid pH Down or a combination of this and standard pH Down (phosphoric acid). Nitric acid is very aggressive and better at buffering carbonates in tap water.
- The very alkaline Shogun Silicon can be used in small amounts instead of pH Up.
In active hydroponic systems the nutrient solution can be run to waste or re-circulated. Generally, run to waste is only suitable for drip irrigation and requires minimal pH management – after all as soon as you have set the pH of a new reservoir of nutrient solution it will stay the same until plants begin to drink. Most hydroponic systems re-circulate the solution and require frequent pH check and adjustments. This is due to the plants in the system actively taking up nutrients and water, which alters the pH of the solution returning to the reservoir.
How often should I check the pH?
For an active hydroponic system you should check your pH as and when you can – but the exact frequency depends on the type of system. You will find that a large volume of water in a reservoir will need less pH adjustments than a smaller volume of water. With this in mind you are able to save yourself from having to regularly adjust the pH by always keeping the reservoir as full as possible. Greater amounts of nutrient solution means the pH will take longer to change.
How often should I adjust the pH?
As the pH approaches its upper parameters (6.5 maximum) you should adjust it back. It is good to allow the pH to drift up and down, as this allows the plant to access different quantities of nutrients at different set points. Setting the pH at 5.8 and allowing it to drift up to 6.6 can often provide better results than constant maintenance at 5.8.
Nutrient Solution Conductivity
Nutrient solution strength plays an important role in maintaining the health of a plant. If the nutrient solution is too strong, the leaves of the plant sometimes become leathery, curl downwards or even burn at the tips. Alternatively, a lower than desired concentration of nutrients will see the plant turn yellow, stretch and become susceptible to disease. The strength of a nutrient solution can be detected using a simple device called a conductivity meter. This indirectly measures the amount of dissolved minerals in the solution – with the more nutrient there is in the water, the higher the resulting conductivity reading.
The electrical conductivity of the nutrient solution is read by a meter and converted into units of measure, the most common values used in Hydroponics being Conductivity Factor (CF), Electrical Conductivity (EC) or Parts Per Million (PPM).
In the UK and Europe, CF and EC are most common, whereas in North America PPM appears more often. The problem with PPM is that there are different scales of conversion depending on the meter – 500 (also called TDS) and 700 – so you absolutely must know which one you’re measuring in! The difference between EC and CF is simply the decimal point (e.g. an EC of 1.0 is a CF of 10). The following chart shows the simple relationship between these values.
As your plants grow, their demand for nutrients will change. Generally, young plants like a weaker nutrient solution and mature plants like a stronger nutrient solution. Therefore, as your plants develop gradually increase the conductivity.
Why do I need to check the conductivity?
Much like with pH, as the plants in active hydroponic systems take up water and use the nutrients, this will alter the conductivity. How much and in what direction it changes depends on the plant and the growing environment. Hungry plants tend to cause the conductivity to drop, whereas thirsty plants cause the conductivity to go up. In ideal conditions and at the right nutrient strength, as the nutrient solution is used by the plant, the conductivity remains the same.
My conductivity is increasing?!?
If your conductivity is increasing, it means the plant is using more water than nutrients. This often comes down to the grow room being too hot and/or having a low relative humidity, so by correcting these environmental problems you can stop conductivity from rising. If you are unable to reduce your temperature or increase your humidity, try keeping your conductivity lower than usual to allow for upward drift and ensure your reservoir remains topped up as much as possible.
My conductivity is decreasing?!?
If your conductivity is decreasing, it shows that the plant is taking up the nutrients from the solution so you need to increase the nutrient strength. This often happens in ideal environmental conditions where there are no excessive external demands on the plant.
Top Tips for Managing and Measuring Conductivity:
- Measure the conductivity of your tap water – this will give you a good indication of your water hardness. A CF of 0-3 is soft water, 4-5 is moderately hard, and 6 and above is considered hard.
- For optimum conductivity control, use a Reverse Osmosis filter to remove all your tap water contaminant – you’ll then be able to start with a conductivity of zero.
- Active Hydroponic Systems that saturate the root zone with oxygen, such as DWC/Bubblers, require a lower conductivity than media based systems such as drip irrigation or flood and drain. This is due the efficiency at which the plants feed in DWC systems, in fact, the conductivity requirements can be as much as 25% lower than other active hydroponic systems.
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