It is a common misconception that visible brown marks or staining that appear on the pool surface is copper staining or has been caused by the copper in the pool. This is NOT the case, since copper doesn't stain brown in colour.
The most common cause of brown marks and/or staining is poor pool maintenance.
Our question is: Are you maintaining your pH correctly and regularly brushing the walls and floor?
We often troubleshoot brown marks in the pool to be tea staining caused from leaf or organic matter that has been sitting on the surface for long periods of time. This is quite common in pools that are surrounded by a lot of debris (trees) or landscaping and are open to the elements such as high winds which will carry dust and dirt that ends up settling on the pool surface.
Most pool owners these days have a robot, suction cleaner or an in-floor cleaning system that helps to keep the pool looking clean. It's not until you brush the pool surface that you realise just how much debris (dust etc) actually lies on pool surfaces.
We recommend regular brushing of the pool surface and walls as part of regular maintenance in order to maintain a clean and sparkling pool.