Some Tips About Chlorination


  • Liquid chlorine (usually sodium hypochlorite) oxidizes everything it can in water — iron, manganese, sulfur, sulfur dioxide (rotten egg smell), etc. — and kills bacteria as well. Put enough chlorine in the water and it will oxidize and kill everything it can, leaving a residual that can be measured with a test kit.  Any level of measurable residual chlorine means that the oxidation and kill have occurred.
  • Most chlorinators use common household bleach, which is typically 5.25% sodium hypochlorite. Look for a generic bleach that isn’t contaminated with additives.
  • Commercial bleach, which is readily available from swimming pool suppliers, is usually 12.5% sodium hypochlorite. One gallon of 12.5% chlorine bleach is approximately equivalent to one pound of dry chlorine gas in treatment capacity.
  • The half-life of a chlorine solution is approximately 30 days, depending upon its concentration, temperature, etc. A 5.25% solution will deplete over 30 days to a strength of about 2.5%.
  • The amount of chlorine solution you’ll need to feed will be a measure of the chlorine demand required for the oxidation/kill and the chlorine residual (the amount extra put in to be able to measure with a test kit). An easily measurable, yet consumer-acceptable, residual is 0.5 parts per million (PPM). If the user objects to the residual chlorine, a carbon filter can be used as a following treatment stage to remove the chlorine.
  • Contact time is an important part of achieving an effective chlorine oxidation and kill. The chlorine solution you inject needs time to thoroughly mix with and treat your water supply. The hypochlorite ions need to make physical contact with the bacteria and oxidizable matter present to react with and nullify them. Hence contact time, or retention time. As a rule of thumb, a 5 PPM residual after 5 minutes of contact, or a 1 PPM residual after 30 minutes of contact, will accomplish an effective oxidation and kill.