pH_concentrate & Dilute Acid

The pH would not be 3. It should be higher than 3.

pH depends on the concentration of hydrogen ions. Sulphuric acid is completely ionized in the solution in the test tube. When the solution is poured into the swimming pool, the number of moles of hydrogen ions keeps constant, but the volume increases a lot. This leads to a sharp decrease in concentration of hydrogen ions, and thus an increase in pH.

The dissolved substances also affect the pH value of the water in the swimming pool. For example, the water would be slightly acidic if chlorine is used as the disinfectant, but the water would be slightly alkaline if a hypochlorite is used as the disinfectant. However, the pH would not be too high or too low due to the large volume of the swimming pool water. (Furthermore, the chloride ions dissolved in water are neither acidic nor alkaline.)

pH value of swimming pool water should be monitored by using a pH meter. pH 3 is a harmful pH value to human beings.