Palintest Photometer DPD No 1 Rapid Dissolve Test Tablets these should be used with Pooltester instruments and will test Free Chlorine from 0 - 5.0 ppm (mg/l) Made in the UK these Test Tablets are considered to be the best available on the market. Storage & Handling - Store in a cool, dry place away from oxidizing and reducing agents, strong acid, alkalis, solvents and organic materials. - Do not mix with other chemicals. - Always wear suitable gloves and eye protection when handling. - Use biocides safely. Always read the label and product information before use.