Chlorine bleach solutions are very effective disinfectants when diluted to the correct concentration. These test strips allowed me to mix a concentration reportedly effective in killing the coronavirus. You never know what your actual concentration is when making solutions with that bleach you bought some time ago, as the bleach degrades over time. I've found that the solutions I've made using the dilution instructions on different bleach bottles yield wildly different concentrations. Now I can use the bleach effectively and with no waste.