Why use chlorine in your spa?
Chlorine is intended as a bactericide for the water of your spa. Ensures proper maintenance and maintains excellent water quality. 
There are two types of chlorine: fast-acting chlorine and slow-acting chlorine. 

The fast-acting chlorine (granulate) is used when the chlorine level must be raised quickly, eg at the start of the spa. Also if you can't treat the water for a longer period of time, it's recommended to perform a chlorine shock with the fast-acting chlorine. 

The slow-acting chlorine (tablets) you use when your chlorine level is up. So first bring your chlorine level is up. So first bring your chlorine level up to the required level with fast-acting chlorine and only then switch to slow-acting chlorine. With long-acting chlorine, the tablets dissolve slowly and this ensures that the chlorine value remains stable (due to weather conditions, for example, this can fluctuate). 

Where should you add chlorine?
Remember the golden rule: never add chemicals such as chlorine and pH directly to the pool or jacuzzi water. Liquid chemicals can be added directly to the water, as they will mix immediately with the water and not sink to the bottom of the pool or jacuzzi. This is because if granules or tablets sink to the bottom, it can cause white stains.

How to prevent this?
Granules: Take a bucket of water from the spa or pool. Dissolve the desired amount of granules and when the granules are dissolved in the water, you may add the bucket amount back to the spa or pool.
Tablets: Place chlorine tablets in the chlorine dispenser. This will distribute the chlorine evenly throughout the spa or pool.