Crush up some vitamin C tablets, put them in a sock, and rub it on the stains. You can also use some ph down in a sock if you have it. If the stain goes away then it is a metal stain. If the stain stays the same then it is organic. If it is organic, take your chlorine up to shock levels and keep the pump running 24/7, brush the pool and they will eventually go away. Let me know if you have any other questions.