Water balancing is the process of maintaining the correct chemical composition of your spa water. Maintaining correct water balance ensures that your chosen sanitizer works to maximum effect.
Correctly balanced water also feels and looks good and protects your spa shell and equipment.
Some sanitising products, notably ecoOne and AquaGarde, reduce the need to constantly monitor the balance of your water because, to a cetain extent, they self-regulate the water. Never-the-less you should still test your water at regular intervals. Then, if something does go wrong you'll be able to correct it quickly before it becomes a problem.
Maintaining the Total Alkalinity within the correct range is the key to water balancing.
If you do this first it's easy!
Maintaining the correct pH will protect the pumps and heater from corrosion and help to avoid problems caused by limescale.
If you get Steps 1 & 2 right you probably won't need to worry about scale, unless you live in a very hard water area.