A lot of of people come into our store looking for advice on how to keep their spas clean. Many of them are looking for an alternative to chlorine, the same-old same-old, or are completely new to the hot tub game. One of the biggest fables in the hot tub industry is that your hot tub can be chemical free with an ozonator and this "special filter," or that this is a chlorine free system. The truth of the matter is there is no real easy to use alternative to chlorine. The main components of spa sanitation are inhibiting growth and killing (shocking/oxidizing) anything that has happened to enter the water alive. Here are a variety of systems that are used for these purposes.
In the past companies like Bioguard and Leisure Time have created systems that use biguanide, which is an organic sanitizer traditionally found in contact lens solutions. Used in tandem with a strong solution of hydrogen peroxide (+30%) as a shock and not compatible with chlorine, Biguanide is at times effective in pools. Though not having the same range of effectiveness as standard tablet chlorine and granular chlorine shock, the ease of use in hot tubs leaves much to be desired. Biguanide in spas will have waterline issues and quickly gums up the filter. Hydrogen peroxide is a potent shock, but it is also extremely dangerous to use as it can easily burn your skin with just a small drop.
Another option is a mineral stick, which uses a zinc and copper as a microb inhibitor, all while still requiring a chlorine/bromine granular to shock/oxidize the water. Some hot tub and online retailers in the past have marketed this with non-chlorine shock (monopersulphate) as a chlorine free system, but this has lead to some sticky situations and skin infections (quite literally). The idea behind the mineral stick is the minerals inhibit the growth of bacteria and other organics. However, this is only effective when used with chlorine and bromine. The stick has to be replaced every month to be kept at an efficient level of minerals in the water.
While a little more expensive than standard chlorine bromine systems, AquaFinesse is both effective at reducing chlorine, keeping water fresh and clean, and not causing any irritation. While a little of chlorine is used (about as much as tap water) to kill bacteria introduced into the water through regular use, AquaFinesse is similar to mineral sticks, but allows for a little more control with out the requirement of shocking the tub everything you get out of it. Furthermore, AquaFinesse is not irritating to the skin and will leave you feeling silky smooth after each soak.