The best product to use is a tablet that is pressed ( not made w/ binders) backed up with liqiuid chlorine as a schocking agent. Schock w/ liquid after heavy usage, rainfall and temps over 92 to 94.
Important to adjust total alkalinity, calcium hardness and stabilizer, which locks the chhlorine residual. The stabilizer prevents the chlorine from burning off due to the UV rays of sunlight.