Copper and iron may be present in sufficient concentrations in the swimming pool water that they cause problems of discoloration. They usually color the water (without making it cloudy) and can stain the swimming pool surfaces as well as the hair and nails of the swimmers.
Testing the pool water will let you know what metal is in the water as well as how much. Copper almost always turns the water green and iron usually results in brown pool water. Iron can also be responsible for a green hue so it is not always possible to make a visual diagnosis.
Copper or iron can find its way into the pool from the fill water. If a well is used, the source may contain these metals in their ionic states. Mains water, while usually well purified, may pick up the metals in the pipe/ plumbing network it passes before it reaches the pool (from rusty or very old piping).
The copper or iron may be the result of corrosion of the pool's pump, heater, pipework or other metal accessories. Nowadays pool water has very little, if any, contact with metal parts unless essential (e.g. pumps are plastic, while heat exchangers have to be metal, usually stainless steel). If the pool's pH is low or the total alkalinity is low or the calcium hardness level is low, then the water tends to be corrosive and the "rusting" of metal parts in the pool is greatly increased.
Another common source of copper is copper-based algaecides. The cheaper ones often supply copper ions rather than complexes and if too much is used, will result in lovely green pool water.
To solve the problem of colored water as a result of metals, there are two general approaches:
Shock treat the pool to oxidize the metal, which then settles out of solution and looks like rust. The rust can easily be vacuumed out of the pool.
Add a sequestering or chelating agent which forms complexes with the metal and prevents it from being oxidized by the chlorine.
Prevent the problem recurring
If the source of the copper or iron cannot be established or if it cannot be avoided, regular addition of a chelating agent or sequestering agent (metal out products) will ensure that any new metal arriving in the pool water will be held in an inactive complex.