ECHA published an update of the List of notifications prepared as of 15 September 2020. For swimming pool disinfection the combination of chlorine (Cl2) and chlorine dioxide (ClO2) can be applied. Chlorine dioxide is added to the water.

More information:
https://echa.europa.eu/documents/10162/27434452/list_of_notifications_en.pdf/0ad3b68a-1e01-304e-722d-f4a8457842c3