So just what is a fusion system?

A fusion system is a form of sanitation for a swimming pool. You have several different ways to kill bacteria in a pool. Chlorine, salt (which is still chlorine), non chlorine chemicals such as Baquacil, and minerals such as the Fusion system.
The Fusion system is a canister that houses a cartridge with copper and silver and has a separate canister that acts as a chlorine tablet feeder. A lot of people think that a salt pool is non chlorine, however a salt water pool takes the salt and converts it into a liquid chlorine. So with a regular chlorine pool and a salt pool you are still testing for 1-3 ppm chlorine in the water.
With a Fusion / Mineral pool you are relying on the minerals to purify the water and this allows you to have the chlorine level at .5 ppm. drastically lower than a salt or chlorine pool. By reducing the amount of chlorine in the water and saves money on chemicals and also has more of a natural sanitation process.
Also, with a Fusion system there is no electrical hook up, no worry about corrosion from salt down the road, and less sanitizer chemicals that are needed for the pool.