Use a sequestering agent to temporarily protect the pool surface.
Sequestering agents are liquid soluble metal chelators added to pool water to temporarily protect pool surfaces from oxidizing metals.
There is widespread misunderstanding in the pool and spa industry regarding the use and effect of sequestering agents. Sequestering agents have been used in municipal water treatment facilities for decades and require highly sophisticated filtration systems for the removal of sequestered metal particles. The size of these sequestered metal particles is simply too small to be effectively removed by pool filtration systems. (The only exception occurs during pool start-ups. When plaster dust from the pool surfaces mix with the sequestering agents, metals tend to stick together in larger particles. Depending on the size of these particles, some – but not all – may be large enough to be removed by the pool filtration system; the smaller particles will simply pass through the filter and return to the pool.) Sequestering agents, therefore, only temporarily bind with dissolved metals to prevent them from oxidizing onto pool surfaces; they do not effectively remove or eliminate metals from the water, and metal stains will inevitably occur.
It is still important to use sequestering agents in your metal control regimen, as they provide needed “insurance” by allowing for the use of the pool while other methods are employed to eliminate the dissolved metals from the water.