After taking up carpet to clean Oak hardwood floor 12 years later we found black spots on floor. They look like someone had installed carpet and pad on a dirty floor. They seem to clean up O.K. but still can see where the spot was. Is this mold or mildew or just dirt? If so what is a good cleaner to get rid of it? Also our cat used a corner for its litter box and left floor stained . Only been doing it for a few months is there something we could use to get it out or do we just replce bad section? I don't know what manufacture or type Oak it is but the wood strips are about 1 to 2 inches wide by 2 to 3 feet long and light color with clear sealer. We really like this floor and would like to get it back to what it once was so, if anyone out there could help, it would sure be appreciated. Thank You in advance.

It is usually from a potted plant they over watered a few times, or where the christmas tree was.

some times and good sand and finish help ,more then likely its a white oak, easy to find , you will still need to sand to blend it all together ,good luck
tommy