My husband put down a beautiful unfinished wooden floor in our
kitchen.  He finished it himself after that.  I purchased Bruce
Hardwood floor cleaner, but I didn't know that you don't use a wet mop
with it.  Well over time, each individual wooden floor piece is
outlined in black.  No other damages occurred.  No swelling, stains,
etc.  How can I get rid of the black between each floor board without
damaging the wood?  I have tried a scrub brush with a light mist of
bleach on it, but I didn't like what might potentially be doing to the
floor.  It looked funny in the area I tried it so I stopped.  I hate
to have to rip up the flooring all because no one every told me how to
clean a wooden floor properly.  Please help!!!

What about sanding the floor?