Do not mix! If you did not stop the leak, clean up the water and Dry the floor right away, you will have exactly what you describe.
First, get some heat on this area, you must get the moisture out of the wood or the area of damage will grow. The black is either tannin staining or mildew. Do not attempt to do any finishing to this area for at least 6 months, It must be dry to about 6% moisture. If the boards have more than 1/16" gaps between them...Replace the area. If the boards are cupped, face nail them and fill the holes with putty, scrape and sand the area. You may have to apply stain to match the patina or stain on the floor.