Free chlorine is the chlorine in water present as hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻), the active forms produced when chlorine gas or sodium hypochlorite is added for disinfection. Drinking water usually carries a residual well under the 4 mg/L US limit. The balance between HOCl and OCl⁻ depends on pH; HOCl, the stronger disinfectant, dominates below about pH 7.5.
In practice
Free chlorine is volatile. Standing water in an open container loses much of it within 24 hours, faster with aeration or stirring. Carbon filters remove it efficiently, and RO pre-filters are designed to strip it to protect the membrane. Ascorbic acid also neutralises it.
Growers dechlorinate mainly to protect microbes in living soil, compost teas or beneficial reservoirs. Direct harm to cannabis at tap-water levels is not well documented. Some hydro growers deliberately add low doses of hypochlorite to sterile reservoirs; that is a separate, deliberate strategy that needs commitment.
Don't confuse with
- Chloramine: chlorine bound to ammonia; stable, does not evaporate.
- Chloride (Cl⁻): the plant micronutrient, harmless at normal levels.
- Chlorine (nutrient): the element as a plant nutrient, a separate entry.
pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.A carbon filter scrubs odour from exhaust air by passing it through activated carbon, which adsorbs aroma compounds such as terpenes.RO water is water stripped of most dissolved salts by reverse osmosis; it has near-zero EC and little buffering, so pH moves easily and Ca and Mg must be added.Living soil is an organic growing medium managed to sustain an active soil food web, so microbes and invertebrates release nutrients and the soil is reused across cycles.Compost tea is a liquid made by steeping compost or worm castings in water, often aerated with food sources, to extract and multiply microbes for the root zone.A beneficial-microbe reservoir deliberately inoculates hydroponic solution with helpful bacteria and fungi so they occupy the root zone before pathogens can; GenetixBay prefers this approach.A sterile reservoir keeps hydroponic solution as free of microbes as possible with oxidising sanitisers or UV, a valid strategy that only works if applied consistently.A micronutrient is an essential element plants need only in trace amounts, below a few mg/L: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel.Chloramine (monochloramine) is a long-lasting water disinfectant made from chlorine and ammonia; unlike chlorine, it does not leave water by standing or aerating.Tap water is municipal or well water used for irrigation; its EC, alkalinity, hardness, sodium and disinfectant vary widely, so it should be tested before use.
