Thoroughly test the water, balance it and remove all metals.
Testing the fill water is an important step in the preservation of your new pool finish
“Recently, many parts of the United States have undergone significant changes in the potable water delivered from local municipalities to the homes and businesses in their water district. Some of the changes have been brought about by drought conditions or extreme flooding and the need to find alternative water sources. Population growth in certain areas has also created the need for alternative sources of water, which can alter the chemical makeup from previously existing levels. Whatever the reason, the need to test fill water should no longer be an option, and it is strongly recommended that all plasterers, builders, service companies, and start-up persons make pre-testing the source water a mandatory requirement in their business practices. This will help minimize the likelihood of surface issues whether a new pool, remodeled pool, or simply a pool that is being drained due to the high mineral composition or cyanuric acid levels of older pool water.
There are a variety of problems that may arise from three fill water factors. These factors are: 1) tap or fill water that is potentially aggressive due to low pH, low calcium hardness, or low carbonate / total alkalinity, 2) tap or fill water that has high pH, high calcium hardness, or high total alkalinity contents, or 3) some fill waters may have elevated levels of dissolved metals in them. The most common are copper and iron, and sometimes manganese. Low levels of calcium hardness, total alkalinity, and low pH can lead to etching of surfaces, dissolution of grouts, and damage to the pool equipment. These problems can be visible in the pool as surface discoloration issues, colored water, and deteriorated metals in pumps, heaters, valves, and other metal components.
High calcium levels, high total alkalinity, and high pH may lead to such problems as scaled pool surfaces, staining discoloration, cloudy water, and equipment issues such as plugged filters and heaters, along with poor circulation.
Dissolved metals in the tap water can lead to colored pool water and staining discoloration of surfaces and grouts.” National Plasterers Council Technical Bulletin Number 1, January 2010