Talked to my cousin that installs granite for a living...
First you need to know what kind of stone as each one is different, but as
@crankcall mentioned checked the instructions.
best way...
- pour some clear water onto a small section
- if the water soaks in and the stone discolours, it means that it's not sealed and time to seal it
- if the water stays on the surface...stone is still sealed and doesn't require anything to be done
He basically said natural stone doesn't need much sealant. But as before...each stone is different so instructions are best.