Especially seedlings and young plants easily suffer from regular watering with pH Down. Add the required nutrients to your water until you have the appropriate EC (nutrient concentration) for your plants. If the pH is still too high add vinegar * or pH DOWN until the solution has the correct pH. If the pH is too low add pH UP until the solution has the correct pH.
When you are using tap water let it sit in a container for a few hours so that the chlorine evaporates. *Vinegar is a neutral acid that is completely harmless to plants when diluted in water. It can be used for Hydrofarms with hydro correls and on rockwool. run a test if you are using coco coir or other substrates. Regularly check the pH and EC of your water if you are using tap water because there are sometimes larger fluctuations in water quality from municipal companies. “Incorrect pH belongs to the most serious nutrient disorders in organic-soil gardens. Many complex biological processes occur between organic fertilizers and the soil during nutrient uptake. The pH is critical to the livelihood of these activities.” (Marijuana Horticulture, Jorge Cervantes) Many plant problems that are attributed by the grower to lack of fertilizer or poor genetics are in actual fact caused by the wrong pH of the growing medium or water (most often of water).
Failure to adjust the pH to the desirable range will result in several negative symptoms, that will range from mild to chronic, depending on the severity and duration of the pH unbalance: single nutrient deficiency or multiple nutrient deficiencies causing any of the following: stunted growth, yellowing, dark blotches on leaves, small dark-blue leaves, contorted shoots, shriveled growth, leaf curl or burn, leaf drop, delayed flowering, low yield, etc. higher ratio of males during sexing appearance of male flowers on females vulnerability to mold and fungus vulnerability to pests. Fertilizing a plant that is suffering from a pH imbalance usually increases the cycle of problems. It may show a brief respite to symptoms, but only because the fertilizer added to the water may have changed the pH favourably for a short time. Without paying attention to the actual problem and adjusting the pH to the correct range your plants will continue to suffer and you will lose yield on a daily basis. Due to the constant availability of nutrients in a solvent form in hydroponics there is a greater range of tolerance in pH fluctuation. Cannabis grows well hydroponically within a range of 5.5-6.5. Usually the pH is regulated to 5.8-6.0 for hydroponic systems with a growing medium that has been stabilized. The ideal pH and pH fluctuation in hydroponics depends on several factors that you have to evaluate on an individual basis because each hydroponic system is different due to the following: water quality growing medium (coco coir, rockwool, hydro correls, mixture of several mediums, other substrates, or mainly pure water such as aero-flow and bubbler) nutrient products used and their buffer capacity additional products or buffer agents used type of watering system & watering schedule EC of nutrient solution size of nutrient solution tank or plant container room temperature size of plants and their nutrient uptake. All of these factors influence how the pH should be adjusted and how it changes in the containers or tank over a period of time. A fluctuation of one full point in hydroponics can usually be tolerated by cannabis as long as the pH is stabilized to the ideal range within 24 hrs. For best results the pH should therefore be monitored daily in a system with large fluctuation. Ideally your water quality should be good enough so that no or only minimal adjustment to the pH is required for a fresh nutrient solution. Purchasing the correct fertilizer for your water quality helps in stabilizing the pH in your system. Several companies offer hydroponic fertilizer for either "hard" or "soft" water. Photo: a standard pH kit for hydroponics includes a liquid pH tester, pH UP (potassium) and pH DOWN (nitric or phosphoric acid) for adjusting the pH range. Alternatively, vinegar can be used on some growing mediums to reduce pH if mineral salts are undesirable due to their effect on the EC of the nutrient solution. Tap water and well water are two main sources that need to be checked for quality. Both can be contaminated with toxic levels of minerals. High levels of sodium (Na) are often found in well water and can cause excessive damage to plants. Photo: yellowing, leaf curl, circular burnt spots on leaves, and leaf drop are typical symptoms from water with a high level of sodium. Tap water can be “hard” from high levels of calcium (Ca) and magnesium (Mg). Chlorine is another common additive which causes stunted growth in plants and acidifies the soil.
If your tap water smells from chlorine you should fill warm water into a bucket and let it sit for a few hours so that the chlorine can evaporate. For a general assessment of your water quality test the pH and EC range with your essential kit.
Also look at the colour of the water and if it has any strong smell. If you notice anything out of the ordinary you can give a 1L sample to the pharmacy for a chemical analysis.