Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

conducts different quantities of electricity. Use a calibrating solution that imitates the fertilizer in the nutrient solution to calibrate ppm or EC meters. Using such a solution ensures the meter readings will be as accurate as possible. For example, 90 percent of ammonium nitrate dissolved in water is measured, and a mere 40 percent of the magnesium is measured! Do not use sodium-based calibration solutions. They are intended for other applications than gardening. Purchase calibrating solution from the manufacturer or retailer when you buy the meter. Ask for a stable calibrating solution that mimics your fertilizer. Calibrate EC and ppm meters regularly. A good combination ppm, EC, pH meter that compensates for temperature costs about $200 and is well worth the money. Batteries last a long time, too.
    1. Hanna 1 mS/cm = 500 ppm
    2. Eutech 1 mS/cm = 640 ppm
    3. New Zealand Hydro. 1 mS/cm = 700 ppm
    Parts per million recommendations are inaccurate and confusing. To help you through this confusion, an Australian friend compiled the following easy reference conversion chart.
    1 mS/cm = 10 CF e.g. 0.7 EC = 7 CF

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    Distilled bottled water from the grocery store often registers a small amount of electrical resistance, because it is not perfectly pure. Pure water with no resistance is very difficult to obtain and not necessary for a hydroponic nutrient solution.
    Electrical conductivity measurement is temperature-sensitive and must be factored into the EC reading to retain accuracy. High-quality meters have automatic and manual temperature adjustments. Calibrating an EC meter is similar to calibrating a pH meter. Simply follow manufacturer’s instructions. For an accurate reading, make sure your nutrient solution and stock solution are the same temperature.
    Inexpensive meters last for about a year, and expensive meters can last for many years. However, the life of most EC meters, regardless of cost, is contingent upon regular maintenance. The probes must be kept moist and clean at all times. This is the most important part of keeping the meter in good repair. Read instructions on care and maintenance. Watch for corrosion buildup on the probes of your meter. When the probes are corroded, readings will not be accurate.
    To check the EC of the nutrient solution, collect samples from both the reservoir and the growing medium. Save time and effort; collect EC and pH samples simultaneously. Collect samples with a syringe or baster at least two inches deep into the rockwool and coco. Collect separate sample from the reservoir. Place each sample in a clean jar. Use calibrated EC meter to measure the samples. Under normal conditions, the EC in the slab should be a little higher than the nutrient solution in the reservoir. If the EC of the solution drawn from the growing medium is substantially higher than the one from the reservoir, there is a salt buildup in the substrate. Correct the imbalance by flushing substrate thoroughly with diluted nutrient solution, and replace with new solution. Regularly check the EC of your water, slab, and runoff.
Hydroponic Nutrients
    High quality hydroponic formulations are soluble, contain all the necessary nutrients, and leave no impure residues in the bottom of the reservoir. Always use the best hydroponic fertilizer you can find. There are many excellent commercial hydroponic fertilizers that contain all the nutrients in a balanced form to grow great cannabis. Quality hydroponic fertilizers packed in one, two, or three-part formulas have all the necessary macro-and micronutrients for rapid nutrient assimilation and growth. Cheap fertilizers contain low-quality, impure components that leave residue and sediments. These impurities build up readily and cause extra maintenance. High-quality, soluble hydroponic nutrients properly applied are immediately available for uptake. Exact control is much easier when using pure high-grade nutrients. Many companies use food-grade nutrients to manufacture their fertilizer formulations.
    Nutrients are necessary for marijuana to grow and flourish. These nutrients must be broken down chemically within the plant, regardless of origin. The nutrients could be derived from a natural organic base which was not heated or processed to change form, or they could be simple chemical elements and compounds. When properly applied, each type of fertilizer, organic or chemical, theoretically produces the same results.
    For a complete background on nutrients and