An owner shall ensure that a certified pool and spa operator: Is on-site at all times when a recreational pool is open; Is available at a semipublic pool, public spa, and at a limited public-use pool for performance of all requirements of this chapter and is able to respond to operational problems within: 30 minutes when not available on-site; or If a contractual certified pool and spa operator, 2 hours when not available on-site; Measures and records, or supervises and verifies the measurement and recording of, all information required in Regulation .46 of this chapter; Performs all duties related to the operation of a pool or spa as required in this chapter; Cleans the filtration system when the filter pressure differential reaches a level specified by the equipment's manufacturer or as specified below: High rate sand filters at 15 psi; Rapid rate sand filters at 8 psi; Cartridge filters at 10 psi; Pressure diatomaceous earth filters at 10 psi; and Vacuum diatomaceous earth filters at 15 inches of mercury; Maintains disinfection residuals according to Regulation .44 of this chapter; Maintains water chemistry according to Regulation .45 of this chapter; and Adds a nonstabilized oxidizer into the pool or spa water equivalent to an amount of free chlorine equal to at least 10 times the measured combined chlorine residual plus sufficient free chlorine to oxidize the ammonia and nitrogenous compounds in the water, on a recommended schedule of once per week for a pool and once per day for a wading pool and for a spa.