Calcium hypochlorite (Ca(OCl)2, HTH, High Test Hypochlorite, Sentry, Perchloron, chlorinated lime, bleaching powder)

This is usually available in granular format or as non-effervescent tablets.  This is often used by military and aid agencies for large scale water treatment.  The US military uses ampoules to ease measurement of chemical needed to treat water trailers, Lyster bags, etc.  It unfortunately leaves a chalk residue that can cloud treated water and gives it a chalky taste on top of the chlorine taste.



Bleaching powder often comes in 33-37% strength and High Test Hypochlorite (HTH) comes in crystal form and has nearly 70% available chlorine.



Either a chlorination test kit is needed to titrate treatment or water can be intentionally over treated and then neutralized with a reducer.



One way to treat clear water is to first make a 1% solution of calcium hypochlorite by mixing 14 gram (one heaping tablespoon of granules) of HTH per quart (liter) of water.  Then adding 11 drops of this 1% solution can to each quart (liter) of clear water.  This produce about 5PPM chlorine, which is equivalent to 5 parts of 1% solution to 10,000 parts clear water.


5mg/L (PPM) concentrations with

Hypochlorite Granules (70% Chlorine)
Liters      Gallons      Grams
250      66      1.4
500      132      3.6
1000      264      7.1
2000      528      14.3
3000      792      21.4
5000      1320      35.7
10,000      2641      71.4


28.3 grams = 2 heaping tablespoons of granules = 1 once



Please note that HTH is highly reactive and can burn or explode if it comes in contact with reducing agents such as sodium thiosulfate, other chlorinating compounds, concentrated acids, and organic compounds such as antifreeze, oil, kerosene and gasoline.  You should never mix HTH with bleach.