Chlorine tablets GRE 0.5 kg20 lTreatment 4-in-1, suitable for swimming pools from 10 to 20 cubic meters. Monthly treatment. Once the chemical runs out, reuse them on the surface alerting you to the need to start a new treatment.Disinfected, algae-free, crystal-clear waterPoolp'o rises to the surface once the chemical runs out, alerting you to the need to start a new treatment.