About 5 years ago I got a new liner for my pool. I have a metals issue which has since periodically stained my liner and I deal with it accordingly but I've noticed when my liner starts to stain I have 3 1 inch by 4 inch rectangles that stain first. They are perfect rectangles. Why would these sections stain first? I know its not one of the higher end liners and we weren't happy with the company that installed it. The questions not why my liner stains but why these sections stand out when they do. Any ideas?