sguingri I have a tile top table with white grout. the best thing i have used to clean it is Westley's® Bleche-Wite Whitewall Cleaner for tires. Just spray it on and let it set for a while. It lefts the stains out and you wipe it off. For scum and lime on shower doors, I have used 0000 steel wool. They look like new!

777sheree "Sealer's Choice Gold" is the best sealer I've found. Highly recommended. Order online, as is professional grade. Paint on with paint brush, wipe off any excess with a rag. I usually do 2 coats, then don't worry for years. Have used on kitchen floor grout as well as bathrooms.