\n| Pre-treatment<\/td>\n | Not always necessary<\/td>\n | Requires a reverse osmosis system<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n The choice should be based on the quality of the available water, the growing system and the fertilisation requirements.<\/p>\n <\/span>What EC should reverse osmosis water have?<\/span><\/h2>\nWater produced by a reverse osmosis system in good condition generally has a considerably lower EC than the incoming water.<\/p>\n As a practical reference, many growers aim for values close to 0.0-0.1 mS\/cm to obtain source water with a low mineral content. However, this range is only a guideline and is neither a universal requirement nor a guarantee of water quality.<\/p>\n The final reading depends on the system, the membrane and the characteristics of the incoming water.<\/p>\n For example:<\/p>\n \n- Tap water:<\/strong> EC of 0.65 mS\/cm.<\/li>\n
- Water after reverse osmosis:<\/strong> EC of 0.04 mS\/cm.<\/li>\n
- Water after adding nutrients:<\/strong> EC of 1.40 mS\/cm.<\/li>\n<\/ul>\n
These figures are provided solely to illustrate the process. The appropriate final EC depends on the plant species, its growth stage, the cultivation system and the fertiliser manufacturer’s recommendations.<\/p>\n It is essential to distinguish between the EC of the source water and the EC of the finished nutrient solution. The former provides information about the initial mineral content, while the latter reflects the total conductivity after fertilisers have been added.<\/p>\n <\/span>Is it necessary to add calcium and magnesium to reverse osmosis water?<\/span><\/h2>\nOne of the most common questions about reverse osmosis water for indoor growing is whether adding a calcium and magnesium supplement, commonly marketed as CalMag, is compulsory.<\/p>\n The answer is that adding an additional CalMag product is not always necessary<\/strong>.<\/p>\nReverse osmosis systems considerably reduce these minerals. However, many complete fertilisers already contain sufficient amounts of calcium and magnesium to meet the requirements of certain crops.<\/p>\n Therefore, before adding a supplement, it is advisable to check:<\/p>\n \n- The composition of the base fertiliser.<\/li>\n
- Whether the nutrient range is designed for soft water or reverse osmosis water.<\/li>\n
- The plants’ calcium and magnesium requirements.<\/li>\n
- The type of growing medium used.<\/li>\n
- The manufacturer’s instructions regarding supplementation.<\/li>\n<\/ul>\n
<\/span>What happens when calcium or magnesium is lacking?<\/span><\/h3>\nCalcium is involved in various processes related to the development of plant tissues. Meanwhile, magnesium forms part of the chlorophyll molecule and plays an important role in photosynthesis.<\/p>\n An insufficient supply may cause growth problems, damage to young tissues or symptoms of chlorosis, depending on which element is deficient.<\/p>\n However, similar symptoms may also appear because of pH problems, salinity, poor root absorption or nutritional imbalances.<\/p>\n For this reason, it is not advisable to attribute every symptom to a calcium or magnesium deficiency without first assessing the growing conditions.<\/p>\n <\/span>Should CalMag be added until a specific EC is reached?<\/span><\/h3>\nThere is no universal EC value that must be reached by adding CalMag before the remaining fertilisers.<\/p>\n Some brands provide specific recommendations for remineralising water before adding their nutrients. Others offer complete formulations that do not require this step.<\/p>\n The correct procedure is to follow the instructions for the fertiliser range being used and consider the actual total amount of calcium and magnesium supplied by all the products.<\/p>\n Adding CalMag unnecessarily may increase EC excessively and cause nutrient imbalances.<\/p>\n <\/span>How to prepare reverse osmosis water correctly for irrigation<\/span><\/h2>\nPreparing reverse osmosis water should follow an organised procedure to avoid dosing errors and obtain a homogeneous nutrient solution.<\/p>\n <\/span>Step 1. Check the EC of the source water<\/span><\/h3>\nBefore adding any fertiliser, it is advisable to measure the EC of the water produced by the reverse osmosis system.<\/p>\n This check helps identify significant changes in membrane performance or the quality of the treated water.<\/p>\n If the value increases persistently compared with normal readings, the system and its operating conditions should be inspected.<\/p>\n <\/span>Step 2. Add calcium and magnesium when necessary<\/span><\/h3>\nIf the fertilisation programme requires preliminary remineralisation, add the recommended product at the dosage specified by its manufacturer.<\/p>\n On the other hand, if the base fertilisers already provide sufficient amounts of these elements, this step may not be necessary.<\/p>\n The dosage must be calculated according to the volume of water being prepared and the product’s concentration.<\/p>\n <\/span>Step 3. Add the base fertilisers<\/span><\/h3>\nFertilisers should be added in the order specified by the manufacturer.<\/p>\n With two-part nutrient ranges, the usual procedure is to add one component to the reservoir, mix thoroughly and then add the second component.<\/p>\n Incompatible concentrated fertilisers must not be mixed directly together, as chemical precipitation may occur and reduce the availability of certain nutrients.<\/p>\n <\/span>Step 4. Mix the solution thoroughly<\/span><\/h3>\nAfter adding the fertilisers, it is important to stir or recirculate the water until the nutrients are evenly distributed.<\/p>\n For larger reservoirs, an appropriate recirculation system may be used.<\/p>\n Mixing should be completed before checking the final parameters.<\/p>\n <\/span>Step 5. Measure the final EC<\/span><\/h3>\nOnce all the nutrients have been added, measure the electrical conductivity of the nutrient solution.<\/p>\n The result should then be compared with the manufacturer’s recommendations and the values appropriate for the plant species being cultivated.<\/p>\n An EC above the target may indicate an excessive fertiliser concentration, while a lower reading may suggest an insufficient concentration. Nevertheless, EC alone cannot confirm that every nutrient is present in the correct proportion.<\/p>\n <\/span>Step 6. Measure and adjust the pH<\/span><\/h3>\nAfter preparing the nutrient solution and checking its EC, measure the pH using a properly calibrated meter.<\/p>\n Many hydroponic crops are grown using approximate pH values between 5.5 and 6.5. However, the optimum range depends on the species, growing medium and nutrient programme.<\/p>\n If an adjustment is necessary, use an appropriate pH regulator, add it gradually and measure again after mixing.<\/p>\n Sudden corrections or excessive amounts of regulator should be avoided.<\/p>\n <\/span>Step 7. Carry out a final check<\/span><\/h3>\nBefore using the nutrient solution, it is advisable to check the pH and EC once more, particularly if several adjustments have been made.<\/p>\n In addition, check the water temperature, reservoir cleanliness and correct operation of the irrigation system.<\/p>\n <\/span>Why can the pH of reverse osmosis water be unstable?<\/span><\/h2>\nReverse osmosis water normally has very low alkalinity and therefore limited capacity to buffer changes in pH.<\/p>\n Furthermore, because of its low ion concentration, some conventional meters may produce slow or unstable readings when placed directly in water with very little mineral content.<\/p>\n Contact with carbon dioxide in the air can also change the pH of this type of water.<\/p>\n For these reasons, an apparently unusual pH reading in reverse osmosis water without fertilisers does not necessarily indicate a problem.<\/p>\n For routine growing purposes, measuring the pH after adding nutrients is generally more useful. At that stage, the solution usually has sufficient conductivity to provide a more stable measurement.<\/p>\n Nevertheless, it remains important to use an appropriate meter and keep it properly calibrated.<\/p>\n <\/span>Is reverse osmosis water better for soil, coco coir or hydroponics?<\/span><\/h2>\nReverse osmosis water can be used in different growing systems. However, its advantages and management requirements are not exactly the same in every growing medium.<\/p>\n <\/span>Reverse osmosis water for soil cultivation<\/span><\/h3>\nIn soil-based growing media, the substrate mixture may provide nutrients and some buffering capacity against chemical changes.<\/p>\n Consequently, using reverse osmosis water is not always essential.<\/p>\n If tap water has suitable characteristics, it may be perfectly acceptable. However, when it contains problematic salt concentrations or high alkalinity, reverse osmosis can make irrigation management easier.<\/p>\n <\/span>Reverse osmosis water for coco coir<\/span><\/h3>\nCoco coir has particular cation exchange properties that affect the availability of calcium, magnesium and potassium.<\/p>\n For this reason, nutrient management in coco coir requires special attention to mineral balance.<\/p>\n It is advisable to use fertilisers designed for this growing medium and follow the manufacturer’s preparation and conditioning instructions.<\/p>\n Using reverse osmosis water does not automatically mean that additional supplements are required if the nutrient formulation already meets these needs.<\/p>\n <\/span>Reverse osmosis water for hydroponic systems<\/span><\/h3>\nIn hydroponics, the composition of the nutrient solution directly influences the root environment.<\/p>\n Starting with low-mineral water makes nutrient management easier, particularly in recirculating systems where certain salts may accumulate over time.<\/p>\n However, regular monitoring of pH, EC, temperature and the overall condition of the solution remains necessary.<\/p>\n <\/span>Can tap water be mixed with reverse osmosis water?<\/span><\/h2>\nYes. Mixing tap water with reverse osmosis water is a strategy that can be used to reduce the mineral content of the starting water.<\/p>\n For example, if tap water has an EC of 0.80 mS\/cm and reverse osmosis water has an EC of 0.04 mS\/cm, a mixture containing equal parts of each could have an approximate EC of 0.42 mS\/cm.<\/p>\n This calculation is only indicative and assumes that measurements are taken under comparable conditions.<\/p>\n However, reducing EC does not guarantee that the resulting mineral composition will be optimal.<\/p>\n If the original water contains high concentrations of sodium, chloride or bicarbonates, these substances will still be present in the mixture, although at lower concentrations.<\/p>\n Therefore, the appropriate mixing ratio should be determined according to the quality of the original water and the requirements of the nutrient solution.<\/p>\n <\/span>How to tell whether a reverse osmosis system is working correctly<\/span><\/h2>\nTo assess the performance of a reverse osmosis system, the conductivity of the incoming water can be compared with that of the treated water.<\/p>\n The approximate salt rejection percentage can be calculated using the following formula:<\/p>\n Salt rejection (%) = [1 – (EC of reverse osmosis water \/ EC of incoming water)] \u00d7 100<\/strong><\/p>\nFor example, if the incoming water has an EC of 0.80 mS\/cm and the treated water has an EC of 0.04 mS\/cm:<\/p>\n Salt rejection = [1 – (0.04 \/ 0.80)] \u00d7 100 = 95%<\/strong><\/p>\nAccording to these conductivity readings, the system is reducing conductive salts by approximately 95%.<\/p>\n However, the expected percentage depends on the membrane model and operating conditions. To assess the system correctly, the manufacturer’s specifications should be consulted.<\/p>\n It is also important to take measurements under comparable conditions, since temperature, pressure and the system’s initial operating period may influence the results.<\/p>\n <\/span>Common mistakes when using reverse osmosis water<\/span><\/h2>\n<\/span>Adding CalMag without checking the fertiliser composition<\/span><\/h3>\nUsing calcium and magnesium supplements without reviewing the nutrient programme may lead to unnecessary additions and imbalances.<\/p>\n <\/span>Assuming low EC means completely pure water<\/span><\/h3>\nA low EC reading indicates low conductivity. However, it does not prove that the water is free from all unwanted substances or microorganisms.<\/p>\n <\/span>Continuously adjusting the pH of water without nutrients<\/span><\/h3>\nThe low buffering capacity of reverse osmosis water may cause variable readings. Consequently, making repeated adjustments before preparing the nutrient solution can complicate the process.<\/p>\n <\/span>Always using the same dosages without measuring<\/span><\/h3>\nCrop requirements change depending on the species, its stage of development and environmental conditions. Therefore, measuring pH and EC should form part of routine growing management.<\/p>\n <\/span>Failing to maintain the equipment correctly<\/span><\/h3>\nPre-filters and membranes require regular maintenance. Ignoring the manufacturer’s recommendations may reduce performance and affect the quality of the treated water.<\/p>\n <\/span>Using water from an ion-exchange softener without analysing it<\/span><\/h3>\nSome domestic water softeners replace calcium and magnesium with sodium. Although they reduce water hardness, they are not equivalent to reverse osmosis systems and may produce water that is unsuitable for certain crops.<\/p>\n <\/span>Frequently asked questions about reverse osmosis water for indoor growing<\/span><\/h2>\n<\/span>Can plants be watered using only reverse osmosis water? |