Hot tub ozonator
An ozonator works by dividing oxygen atoms in the water into free atoms that then collide and recombine, producing oxidizers and lowering the need for chemical water treatment.
The ozonator will do its job only when it is turned on, using electric power. Once turned off, the water returns to it’s former level of purity.
The ozonator can consume quite a lot of electrical power. Using bromine or chlorine is much cheaper. If money is a problem, then the ozonator can be neglected. Either way, it is more a case of preference than need.