Commercial/public pools in many countries in Europe follow the DIN 19643 standard which is lower levels of chlorine (0.3 to 0.6 ppm without ozone; 0.2 to 0.5 ppm with ozone) with no CYA combined with coagulation/filtration and granular activated carbon (used to remove THMs and other DBPs, but also removes chlorine with each pass). As for residential pools, I don't know if hydrogen peroxide is popular in Spain.