Black rust or Ferrous Oxide

This is what happens within days of placing a Merus ring near water. We placed a jar of tap water on a Merus ring. We placed some rusty old steel parts in the water. this picture was taken on the third day. The rust is being softened and returned to suspension.
If you look closely you can see a rusty sludge is forming some millimeters thick on the bottom of the jar. Where the rust has been loosened enough to fall away, you can also see some black areas. This is Ferrous Oxide, which replaces the rust and forms a black protective coating on the steel, protecting against further rust.
Black rust forming on steel.
Activated merus water.