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What is background conductivity and what is good water?

The best water for your hydroponic gow room is the purest water, one with the lowest amount of unwanted salts and other containments. Background conductivity is the measure of the conductivity of the water before anything hydroponic nutrient is added. The 'background conductivity' of your water is measured in the same way you would measure a nutrient solution. Rain, desalinated or R.O water and distilled water are all excellent as they have very low background conductivity. Tap water can vary from excellent to unsuitable. Generally, the best results will be with water where the background conductivity is below 150ppm. The maximum acceptable background conductivity reading the less room there will be for the nutrient and additives. Some areas are known to have hard water. The bottom line is you should get the best water possible. Better grow room results ALWAYS come from better water, everything else being equal.

I have been told my area has hard water. What does that mean?

Hard water is generally considered to be water that contains more than 60ppm dissolved calcium and magnesium. The problem with hard water is that it also contains many other different types of contaminants in amounts which vary greatly depending on the water source. The ratio of calcium to magnesium also varies from one location to another. Even within a single city you may find large variations as cities often have more than one water source. It is for this reason that there is no one hydroponic nutrient that can compensate for hard water in all areas. While both calcium and magnesium elements are the most common in hard water (they are also plant nutrient elements), if there is too much of these elements, the nutrient solution will be out of balance which can lead to serious deficiencies. The other problem is hard water usually has a high pH and a heavy load of bicarbonates that cause another problem, pH control. For example, in the run to waste, some very hard water may require an input pH 4.0 and may run off at pH 8.0 giving an average of Ph 6.0. At these levels you are going to require a lot of acid. In addition, your hydroponic nutrient solution may become unbalanced because of the amount and type of acid used. The best way to solve this problem is to get better water where possible.

Is soft water always good water?

No, Soft water by definition does not contain significant amounts of Calcium and Magnesium salts but it may contain detrimental amounts (>350ppm) of Sodium Chloride and still be soft. Soft water is definitely easier to use in your grow room than hard water provided the unwanted salt levels are not too high. The main advantage of using soft water is that it is easier for managing Ph.