Using Spa chlorinating granuales is one of the worst things you can use in a spa or hot tub. Within a week or two of using, the ability of the chlorine to oxidize and sanitize the water is greatly diminished. This is due to the chemical that holds the chlorine molecules dissolving and building up in the water which requires draining the water every 2 -3 months and is a common cause of hot tub rash.
Use household bleach for maintenance instead and your water will be cleaner and clearer for longer periods of time. It can also help make your water more comfortable and reduce itching.