Chlorine shock or chlorine granules will both oxidise and disinfect the water, this is best used when you first start up your hot tub, changed the water or it needs a good clean. As you will be using higher dosage of chlorine it is not recommended to be used all the time and only now and again, as the chemicals can be hard on your components (you are advised to remove headrests when shocking your hot tub). For shock dosage refer to your instructions on the bottle.
Non-Chlorine Shock is an oxidiser that will directly oxidise the waste itself, however it does not disinfect the water. This is ideal to use in hot tubs with heavy usage, it eliminates waste and odour in the water before it takes hold. You can also use this with new water and/or add a dose on a weekly basis to prevent your water from deteriorating. Add after bathing as instructed on the bottle with the circulation pump running. To be used in conjunction with your preferred sanitiser.