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Standard pooltesters use DPD as an indicator, which is not effective above around 10 ppm. To access a higher range you need to use a different chemistry.

For example, Palintest manufacture a chlorine high range test which is effective up to 250 ppm, based on potassium iodide chemistry - this is available in comparator or photometric formats. The range that you mention goes up to 5000 ppm, so you would need to dilute by 20x in order to bring into range.