My husband & I were looking up under our carpet. We found out we had oak hard wood floors that have never been sanded or finished. So, we decided to go with the hard wood floors and remove the old carpet,(which we were getting ready to replace). Now, that we have pulled up the old carpet there were a few water spots and animal stains. I mean, this house is over 30 years old and to have a few spots, the flooring is in very good shape. I was shocked! Now, I am trying to sand and get the floor ready to be finished. I don't know if I should remove the bad spots or sand them. I would like to know what grade of sand paper should I use? What else can I use to get the bad spots out instead of replacing the flooring?