eeek, I missed the 5 copper Waterbear is right, drain and refill. You may have other metals in your fill water, but they can be controlled with sequestering agent. You have to check the trichlor - a lot of it has copper in it now - it is used as an algaecide. Also with the trichlor it makes the water very acidic which can eat the copper element in a pool heater. Brown stains are ususally iron, which is very common in well water.