Iron In Closed Loops
Why Won’t The Iron Filter Out?
You may have colloidal iron. This will look like red-water iron but cannot be easily filtered. The iron has precipitated (turned to ferric iron) but the molecules formed do not stick together to form large enough pieces to settle to the bottom of a container or be trapped with normal filtration. This water/solid combination is called a colloidal mixture.
To test if you have this type of water, collect a sample in a clear glass container. Shine a flashlight beam through the water and see if you can see the light in the water. Then, let the water set overnight. If after setting overnight you can still see the beam of light as it passes through the water and there was no settling of material on the bottom of the container, the chances are very good that you have colloidal iron.