A low sludge trivalent chromium based conversion coating bath is provided which forms corrosion resistant coatings on aluminum and aluminum alloys by contact with the bath, which is suitable for use as a rinseable or dry-in place conversion coating for metal, that comprises trivalent chromium cations, fluorometallate anions, guanidinium ions and at least one organic anti-corrosion additive, and other optional components, as well as methods of making and using same, and metals coated using the compositions, the coated aluminum serving as an effective base for paint primers.