Hi Peter, please check your ...

Hi Peter, please check your calculations for dosing sodium hypochlorite.  If you have a 3.5% solution (normal household bleach) this equates to 0.35 g in 10ml.  when this is added to 20 litres it gives a concentration of 17.5 mg/l, which is quite high and people are likely to avoid dosing as it will give a strong chlorine taste.  We had usually recommended adding 1 teaspoon to 25 litres which gives a concentration of about 7 mg/l, still quite high but allows for some degradation and random measurements.