■Why measure every hour during class? Even if the standards are met before use, it is necessary to check every hour on the day of use because many students enter at once. Free residual chlorine should be measured at least once every hour during use, with a desirable upper limit of below 1.0 mg/L. The measurement points should be three locations that are almost evenly spaced along the diagonal, about 20 cm below the water surface. ■Estimate the dosage through calculation 1 mg/L corresponds to 1 g per cubic meter of water. For example, to raise the chlorine level by 0.3 mg/L in a pool with a water volume of 400 cubic meters, you would need 120 g of effective chlorine, which is about 1 kg if using a liquid with 12% effective chlorine. Calculate based on the effective chlorine indicated on the product, and measure again after the concentration has become uniform. Continuous injection of chlorine is the preferred method. Even if not using continuous injection, it is necessary to maintain a uniform concentration of free residual chlorine. ■What should be recorded together? Record the results of free residual chlorine, pH value, and clarity along with the number of swimmers, usage time, air temperature, water temperature, and the status of disinfectant use. Records of regular inspections should be kept for five years, and daily inspection records should be maintained for three years.

■Do not mix chlorine agents! The chlorine agents that can be used according to standards are sodium hypochlorite solution, calcium hypochlorite, or chlorinated isocyanuric acid. Mixing different types can cause a rapid reaction and may lead to an explosion, so caution is necessary when handling them. Ensure that the dedicated chemical storage is structured so that swimmers cannot easily access it. ■Is the air in indoor pools monitored? In indoor pools, the desirable level of chlorine gas in the air is below 0.5 ppm. If it exceeds this level, ventilation should be performed, and checks should be made to ensure that chlorine agents are not in contact with other chemicals. ■What to do on water drainage days? Even at normal residual chlorine concentrations, there can be toxicity to aquatic life. Therefore, before discharging directly into public water bodies, neutralize with sodium thiosulfate or leave it in a drainage tank for more than a day, and confirm that the residual chlorine has decreased using methods like the DPD method. Similarly, after using a large amount of chlorine agents for pool cleaning, the drainage should be treated in the same way before being released. ■Consultation on pool chemicals At Torii, we offer consultations on chemicals used for managing school pools, such as lightweight solid chlorine agents. Please feel free to reach out to us for inquiries.