There are loads of different chemical systems available for your hot tub, and finding the one that suits you best is key to Hot Tub Happiness.
1. High Chemical, Low cost.
This system can be either Chlorine or Bromine and is marketed in a lot of confusing ways, Like Beachcombers Bromo blast, or Lithium.
It simply uses high chlorine or Bromine levels (around 3-5 ppm) to kill anything in the water. It is reliable and relatively inexpensive, but it is harsh on skin, high Chemical smell, and requires quarterly draining of the water.
2. Low Chemical, Low to Mid cost.
Enzymes like Spa marvel, or Spa Perfect natural seaweed and many others fall into this class and having tried most of them them all the Spa Marvel is far and away the best of the enzyme group.
It allows you to go to 1-2 ppm of chemicals and is mild on the skin, low odor and allows you to go 8 to 10 months between water changes.
3. Super Low chemical, expensive.
Mineral salt sanitizes like Aquafiness and Mineralux, and are simply amazing. and of them all Aquafinesse is far and away the leader, it is actually used in hospitals in Holland to treat eczema on new born babies!
It allow you to go to drinking water levels (around 1ppm) of chlorine, it is mild and actively help your skin by replacing natural minerals into the epidural layer. It also can keep your water great for up to a year!