Hi Anvar,Please see the below ...

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Hi Anvar,

Please see the below reaction below to answer your question. Dosing Cl2 gas and ClO2 will decrease the pH and NaOCl will increase the pH. And also, sodium hydroxide is a stabilizer for NaoCl, which increase the pH even more. 

Cl2 + H2O→ HOCl + H+ + Cl–

2ClO2 + H2O→6 ClO2– + ClO3– + 2H+

NaOCl + H2O → Na+ + HOCl + OH–