We had some down time with our spa a while back and took the opportunity to re-grout the tile. The grout was in fine condition, but it was discolored and made the tile (and therefore the spa) appear less-than-pristine to our customers when full of water. In reality the spa and water was beautifully healthy and clean, but the grout staining really played tricks on the eyes of our loyal soakers. You can see the difference in the pictures below that were taken mid-process. This was a cheap, quick, and easy initiative. Good luck and keep 'em safe!