Best sealer for shower floor

This is a beginner question.
Have a shower floor with ceramic tile and grout. When put in about 7 years ago I vaguely remember the contractor saying that it should be sealed every ____ years.
Well, now some of the grout seems to stay dark (wet) for a long time after a shower. So I was planning to put down some tile and grout sealer.
Picked up some TileLab Tile and Grout sealer at Home Depot.
But now thinking I should get some advice from this group before proceeding.
Is that a good product or is there something else I should use?
Thanks for any tips.
Please send email to: nwhiii at yahoo dot com

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