In order to get accurate measurements when testing phosphates, extra care needs to be taken with the preparation of cells / cuvettes.
A number of tablet reagents used for other tests, eg DPD tablets, contain phosphates. Some tap water also contains phosphates.
- Not use cells / cuvettes that have just been used for chlorine testing, as these phosphates can stick to the tubes, resulting in an incorrect reading
- Keep a set of cells especially for Phosphate testing only
- Rinse cells with deionised water straight after testing and allow to drip dry
- Occasionally rinse cells with vinegar to remove any build-up of deposits
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