Chlorine tablets in a 500g screw top tub.
Complies with European standards:
EN1040 at 0.0068% in 48 litres of water
EN1275 at 0.0136% in 24 litres of water
EN1276 in 5mm at 20oC in conditions of cleanliness at 0.0166% or 1 tablet in 20 litres of water.
EN1650 in 15mm at 20oC in conditions of cleanliness at 0.08% or 1 tablet in 4 litres of water.