There are times when your swimming pool will change colors after adding chlorine or shocking your pool. The colors may vary from green, red, brown, purple or black. The reason behind this color change usually indicates the presence of minerals (metals) in your swimming pool. The chlorine added to the swimming pool oxidizes the metals and will cause a chemical reaction that becomes visible in your swimming pool.
Click Here for Metal Sequestrant (Used for Iron, Manganese, Copper, and Calcium)