The strength of the nutrients in hydroponic reservoirs will determine if your plants will be healthy, malnourished, or overfed. If the nutrient level is low, the plants will have stunted growth and delayed flowering. Likewise, the plants will suffer nutrient burns if the nutrient concentration is too high.
PPM in hydroponics indicates the total dissolved solids (TDS) in hydroponic solutions in parts per million. Electrical conductivity (EC) rises when nutrients, salts, and other concentrates are added to water. EC tests show ion concentrations, which also signify TDS levels, interpreted in PPM.
Instead of operating your hydroponic system blindly, PPM shows you what your plants are feeding and if they are absorbing enough. The rest of this article will further explore PPM in hydroponics, its connection to pH, and the impact of PPM levels on the plants you are growing hydroponically.
Understanding PPM (and Other Common Terms) in Hydroponics
PPM, EC and TDS are common terms you will come across when measuring nutrient concentration in hydroponics. Electro Conductivity (EC) and Parts Per Million (PPM) are the main units that show ion levels and the total dissolved solids (TDS) in a hydroponic reservoir, respectively.
EC is usually the preferred measure of TDS because it is a universal unit. Depending on the instrument you are using, Electro Conductivity may be displayed as EC or EC x 1000. For example, if your TDS tests show a 2.0 EC, it is the same as a system with a reading of 2000 EC.
PPM is acceptable, but unlike EC whose units are standardized, PPM has three conversions (US, Australian, and European standard), which is evident in the meters, depending on where the manufacturer is based.
For example:
- Hanna TDS Meters 1 EC = 500 ppm
- Eutech meters 1 EC = 640 ppm
- Truncheon meters 1 EC = 700 ppm
PPM is sometimes considered unreliable because you may not know which conversion was used. Most nutrient meters give calibrated readings in EC and PPM. It’s easier to determine if the hydroponic solution is ideal or if the concentrations need to be altered to ensure optimal plant growth.
The differences in PPM due to multiple conversion options is one of the reasons PPM for various hydroponic plants is given as a range and not an exact PPM. For example, basil does well in hydroponics systems with a PPM of 700 – 1200, while common beans need a higher PPM range of 1400 – 2800. The range accommodates differences in PPM meters.
CF (conductivity factor) is another reading you will discover in some meters. Like EC, the CF reading shows concentration levels of TDS in hydroponic solutions. The difference is CF is 10 x the EC reading. So, CF eliminates the decimal point from the EC. For example, if the EC reading is 0.2, the CF reading is 2.
This video is a great resource on Electric Conductivity in hydroponics:
The Importance and Benefits of PPM
Nutrient demands of hydroponic plants change as they grow. However, you can’t keep guessing how much the plants have consumed and how long it takes them to deplete the nutrients in the hydroponic solution. That’s where PPM steps in to help you out.
Here are some of the ways PPM in hydroponics is so important and beneficial:
Monitor Plants’ Nutrient Needs
PPM allows you to keep track of the growing nutrient needs of the plants. In particular, it lets you know when to feed your hydroponic plants and how much food to add to the hydroponic solution.
Better Tailor Nutrient Concentrations
You can tailor nutrient concentrations to suit the type of plant and the different stages of growth. For example, as plants transition from vegetative to the flowering stage, they require more nutrients, so you need to check the PPM of the solution and verify the ideal PPM for the plant when it starts to flower.
Identify High or Low Concentrations
PPM lets you know when nutrient concentrations are too high or too low. Instead of waiting to notice stunted growth or nutrient burns, you can ensure crops remain healthy throughout your growth cycle by checking PPM regularly.
Know When to Replenish the Reservoir
Since plants consume the nutrients from the hydroponic solution, PPM makes it easier for you to plan when to replenish the hydroponics reservoir.
Monitor Your Water Status
You can tell the status of the water you use for your hydroponics project. Pure water has no impurities, so it doesn’t conduct electricity.
Most manufacturers of hydroponic nutrients assume you’ll be using water with zero EC. Some types of water have high concentrations of TDS, while others have low concentrations. Unfortunately, some of the minerals in water don’t add value to the plants.
What Changes in PPM Mean
When planting crops hydroponically, you have to keep checking the PPM of the solution.
The changes you see have several implications:
A Consistent PPM
If the PPM remains the same over a long period, the plants are consuming water and nutrients equally. This shows the solution strength is ideal, and you should endeavor to keep it that way.
A Drop in PPM
If the PPM drops, the plants are using up more nutrients than water. This shows the plants are underfed, so they consume whatever they can. You should consider increasing the solution strength by adding more nutrients. However, you need to monitor the plants to ensure they don’t suffer from nutrient burns.
A Rise in PPM
If the PPM increases, the plants are consuming more water and leaving more TDS in the solution. It’s also possible that you’re overfeeding the plants, and more water should be added to dilute the hydroponic solution.
However, if temperatures have been high, the plants may have been thirstier than usual. Check to see if the plant root systems are healthy, as they may not be absorbing nutrients as expected.
What Is a Good PPM for Hydroponics?
Hydroponic plants have different nutrient demands. Testing PPM and tailoring solutions to suit the needs of the plants you intend to grow hydroponically will guarantee a high yield, and you will be able to harvest the plants within the expected period.
A good PPM for hydroponics ranges between 560 to 1400 depending on the plant’s needs. Plants like artichoke and asparagus require a nutrient concentration of 860 – 1260 PPM, while celery, cucumber, cauliflower, and spinach require 1260 – 1400 PPM. Lettuce is one of the plants with the least nutrient demands at 560 – 840 PPM.
Manufacturers give instructions on the nutrients to add per liter of filtered water. Measuring PPM is important because the water you use will affect PPM.
Tap water has minerals, so it has conductivity before you add nutrients. Pure filtered water has no conductivity, so PPM is zero. If you add the same amount of nutrients in filtered water and tap water, the solution containing tap water will have a higher PPM.
How EC Factors Impact PPM
Electric conductivity in hydroponic solutions increases or decreases for various reasons. You should aim for a stable environment to ensure the hydroponic plants absorb nutrients easily at all times. A rise in EC implies an increase in ions due to high TDS. This will have a direct impact on PPM.
Factors Affecting EC
The factors below will all have an impact on PPM. When choosing the hydroponic nutrients, you need to make sure the components are suitable for different stages of plant growth. Nutrients with more ions are absorbed more readily by plants as long as the pH levels are ideal.
Temperature
A rise in temperature in the hydroponic solution will cause electric conductivity to increase.
Salt Concentration
The higher the nutrient concentration in the hydroponic solution, the higher the electric conductivity. The number of charged ions increases when you add nutrients to the water. This increases TDS and, ultimately, PPM.
The Type of Salt
Nutrients act as salts when put in water yet are of different weights and ion levels. For instance, 500 ppm sodium chloride solution has 30% more ions than potassium chloride solution. Likewise, a 500 ppm potassium phosphate solution has more ions than the sodium chloride solution.
Nutrients and Electric Conductivity
When you add hydroponic nutrients to the water, you are adding salts that will break down into positive and negative ions. For example, when NaCl is added to water, it breaks down to Na+ and Cl– ions. The ions conduct electricity, so the more salts you add to water, the higher the electric conductivity.
EC is an indicator of the ions in the hydroponic solution. The higher the salt concentration, the higher the EC. Likewise, the lower the salt concentration, the lower the EC.
When you over-fertilize your hydroponics system, you will be adding too much salt to the system. This will cause osmotic stress, nutrient imbalance, and ion toxicity in the hydroponic system. Since TDS levels will be high, the PPM reading will be high.
Signs of High and Low PPM in Hydroponics
Plants usually communicate when something is wrong. Before you test the solution’s PPM, you will notice changes in your hydroponics plants. Once you see unusual changes in the plants, you’ll need to test for PPM levels to confirm your suspicions.
Low PPM
If the PPM is low, some of the common signs in hydroponic plants are:
- Stunted growth
- Poor root development
- Some leafy vegetables will have small leaves when they should have larger, more mature leaves
- Low crop yield
- Brown spots or holes in leaves
How to Raise PPM
When all conditions in your hydroponic setup function optimally, the PPM will drop over time. This is because the plants keep consuming the nutrients.
As they grow, their nutrient demand increases. When PPM drops, you need to add more nutrients to your hydroponic setup.
Avoid adding fertilizer directly into the hydroponics system. Instead, mix the nutrients into water and add that into the reservoir a little at a time. Measure TDS to confirm PPM levels are within acceptable limits. Repeat this process until you get the right PPM levels.
High PPM
When the PPM is above the recommended levels, you should notice:
- Roots that are too thick
- Leaf discoloration
- Wilting of leaves and stems
- Burnt leaf edges
- Fast growth but poor quality plants
- Dull appearance when leaves are usually shiny and vibrant
Test the solution’s pH and PPM when you notice these signs in your plants. Sometimes plants fail to absorb nutrients because the solution is too alkaline (high pH). Likewise, nutrient levels fall when the pH is too low (too acidic), thus affecting PPM levels.
How to Lower PPM
Your hydroponic reservoir’s PPM may be high because the water you used already had high concentrations of TDS, you put in too much fertilizer, or the plants consume too much water and leave behind high TDS concentrates.
You can lower your hydroponics system’s PPM in several ways.
Add More Water
You can add more water to the hydroponics reservoir. You can give your plants instant reprieve by diluting the solution. This will reduce the nutrient-to-water ratio significantly and ultimately lower PPM.
Use Reverse Osmosis
Use reverse osmosis systems to reduce TDS concentration. Heavy duty water filters will separate nutrients and the water forcefully. While this may increase the cost of running your system, it’s one of the most sustainable ways to maintain optimal PPM levels in your hydroponics system.
Check pH Levels
Sometimes high pH levels cause the mineral content to rise because it limits mineral solubility. Nutrient uptake diminishes, and PPM increases when the hydroponic solution is too alkaline. You may be able to lower PPM by lowering the hydroponic solution’s pH.
The Relationship Between pH and PPM
For your hydroponic system to function optimally, the conditions must be ideal. If you only focus on temperature, grow lights, and feeding cycles but ignore pH and PPM, you’ll likely notice low yield and poor plant quality because the plants aren’t absorbing the nutrients.
The ideal pH for hydroponics is 5.0 to 7.0, depending on the plants. Some plants, like tomatoes, perform well in slightly acidic solutions (5.0) than lettuce which requires a more neutral pH of 6.0 to 7.0.
Impact of pH Levels on Hydroponics
| pH Level | Impact On Hydroponics |
| 4.0 and lower (too acidic) | Root damage |
| 4.0 – 4.9 | Nutrient leaching |
| 5.0 – 5.9 | Good pH and great nutrient absorption levels |
| 6.0 – 6.5 | Ideal pH |
| 6.6 – 7.0 | Acceptable balanced pH |
| 7.1 – 8.5 | High basicity leading to poor nutrient uptake |
| 8.5 and above | Root damage |
At a glance, a change in pH appears to be a drop in one number. However, one pH value represents a tenfold difference because pH is a logarithmic measurement.
For example, if the ideal pH for the hydroponic solution is 6.0, but the reading shows 5.0, it means the solution is ten times more acidic than it should be. If the reading is 4.0, when the best pH is 6.0, the solution is 100 times more acidic.
PPM and pH
pH and PPM are connected because the hydroponic solution’s pH level will determine nutrient absorption levels. The absorption of most nutrients is optimal when pH is neutral at 7.0. Plants easily absorb nitrogen, potassium, sulfur, calcium, magnesium, and manganese when the pH is 6.0 – 7.0.
If you measure PPM in this hydroponic system, it’s likely to remain constant for some time since the plants will be absorbing water and nutrients at an acceptable rate. However, PPM will start dropping as the plant’s nutritional needs grow.
Manganese, boron, and iron solubility and root uptake fall significantly when the pH is too high (7.5 – 9.0) but increases in lower pH levels. On the other hand, phosphorus and nitrogen solubility and absorption rates also drop at pH 8.5 and pH 6.0.
When hydroponic plants are not absorbing nutrients, they’re most likely absorbing more water to stay alive, increasing PPM. Unfortunately, this affects yields, and the plants will appear unhealthy.
It’s important to note that you can have the wrong hydroponic pH even when your PPM reading is right. For instance, your solution mix may have the ideal PPM of 700, but the pH may be lower at 4.5.
The implication is that TDS is likely made up of heavy metals, which will toxify the plant if pH levels remain the same. You’ll need to adjust the solution’s pH upwards to improve solubility.
A hydroponics ph Up and pH Down solution instantly raises or lowers pH, depending on what you need to do. If the pH is too low, add a few drops of pH up and test to check if pH is at the right level. If it goes too high, you can lower it by adding a few drops of pH down.
This YouTube video illustrates the relationship between PPM and pH and why both values matter in hydroponics:
How Often Should You Refresh the Nutrient Solution?
Check the PPM and pH in your hydroponics system regularly will let you know if the nutrient solution is still working for the plant or if you need to make changes. High or low PPM and pH levels will result in deficiencies and toxicity within the hydroponic system. The PPM results will tell you if the solid concentration is too high so you can dilute it.
You should refresh your nutrient solution as often as needed using changes in pH and PPM as a determinant. High PPM is quickly fixed by adding water with the right pH, while low PPM requires adding more nutrients. In general, it’s best to replace the entire hydroponics solution every two weeks.
You can keep your hydroponic system from demanding too much of your time by ensuring the system is well balanced from the get-go. Use filtered water and check the pH before adding hydroponic nutrient solutions. You should also add the nutrients according to the hydroponic plant and confirm the PPM levels are within the required range.
Why Topping-Off Water Is Important in Hydroponics
Topping-off water in the hydroponic reservoir is the natural first reaction when you notice a drop in the reservoir. Making another mix of hydroponic solution and adding it to the reservoir before testing PPM can cause the system to be overloaded with salts and heavy metals.
Topping off the water in the hydroponic system is important because:
- Some nutrients, like copper, zinc, and nitrogen, are not absorbed as readily as water. Adding more nutrient solutions will increase the TDS significantly, raising PPM levels beyond acceptable levels.
- Adding plain water is safer for the plants, which may be distressed if you add more fertilizer.
- Nutrients in hydroponic systems last for 7 – 10 days. Topping off the hydroponic reservoir may be necessary every 2-3 days.
It’s a good idea to keep track of the water you’re topping off. When the volume is the same as that of the hydroponic tank, consider making a nutrient mix to charge the system. By the time you’ve topped off this much water, all the nutrients would have been utilized or diluted to levels that would affect your plants.
Conclusion
PPM, like pH, is one of the values you shouldn’t overlook in your hydroponics systems. It helps you keep track of the TDS in the system, which is primarily made up of the nutrients you added.
Notably, PPM is the backbone of your hydroponics system, as it lets you know when to feed your hydroponic plants, if your plants are absorbing the nutrients well, and when to add water to the system.
