We have several fish oil stains that have soaked into our hardwood floor. I have tried to clean it and sand it out but it does not seem to be coming up. If I can't get it out, is there a way I can cover it up with special oil or sealant? We just moved into the house, so I couldn't tell you the most recent time it's been sealed.
This can be more art than science for fixing small spots like that. A lot depends how far into the wood the oil penetrated. Often it can become a matter of spot sanding, staining, refinishing...
Two pretty safe options are baking soda & dawn. Start by putting 1/8" or more baking soda over each of the oil spots. Leave it a few hours to overnight. If that worked, you can try it again. Make sure to vacuum it very well.
After the baking soda, mix a couple to few drops of regular Dawn (not ultra, etc) into a glass of room temp to warm water. Use a cotton ball or q-tips to clean the area following the grain.
Between the above, this should take care of cleaning the surface. Do not use a brush or anything abrasive as that will hurt the finish.
Before recommending any other type of cleaner/de-greaser, we would need to know what kind of stain finish you have. Otherwise, it's easy to make it worse.
Do you know anything more about the floors? Do you have an inconspicuous area (e.g. closet) where you can test cleaners for compatibility (better safe than sorry, those are nice floors)...