Short answer
Use test strips made for the sanitizer you use: dip one in the solution and compare the colour to the chart. Chlorine, quaternary ammonium and iodine sanitizers each need their own strips. The correct concentration and contact time come from the product label, and your health unit may set its own range.
Test every time you mix a new batch for a sink or bucket, and again during service, because the concentration drops as the water gets soiled. For a low-temp dishwasher, test the final rinse water regularly to confirm the chemical pump is working.
Too weak and the solution does not sanitize; too strong and it can leave residue on food-contact surfaces and irritate skin. Measure the chemical rather than pouring by eye.
Store strips dry and check their expiry date. Many kitchens keep a simple log of readings, which shows an inspector the routine is being followed.
Updated · By Norpex