The make up of the mains water supply can vary considerably across the country; you may even have a non-mains source such as spring or well water. As a result, different levels of pH, total alkalinity, calcium hardness and mineral content will be found in the water that you fill your spa with. In hard water areas of the UK or if there is a high mineral content, it is strongly recommended that Fi-Clor Spa Anti-Scale is added when your spa is initially filled with fresh water and also every time it is topped up or refilled after periodic draining. This should help to minimise scale formation and staining of the spa surfaces.