is there something you can put on mold floors to get rid of it
The moisture usually comes from above, seeping through the finish and soaking into the wood, but it can also come from below, if the subfloor is wet. You can kill the mold and get rid of some of the discoloration using wood bleach, but you may have to stain and refinish the floor -- or part of it. There is a big difference between black discoloration that has settled on the surface of your oak flooring and in a discoloration of the wood itself. You can attribute the problem to moisture in both cases, but in the first instance, remediation is fairly straightforward and doesn't involve sanding or refinishing.