Sealing grout

Crysgrits

I apologize if this question is answered somewhere else....I can't seem to find it though. Can anybody recommend a good grout sealer? I recently had my bathroom re-tiled (including shower) and I cannot seem to get the grout in the shower to stay sealed. I have already tried several coats of Aquamix and for the most part it seems to work, but has "lost the effect" within a matter of just a few weeks. There are also a few places where I don't think it has ever actually been sealed. I have followed the instructions very carefully, as I know that when done properly, this really should only have to be done 1-2 times per year. I have already sealed it 3 times in 6 months, and yet again, my nice light grey grout is almost black....I promise I am not that dirty!! I believe my tile is stone, and the grout is sanded. Is there something wrong with the grout??? or the application?? I have been using the Aquamix grout sealer, and applying with a foam brush. and I let it set for at least 48 hours before I use it again.
Somebody please help. Thanks.

Bud Cline

What makes you think it isn't working? It's working.

Crysgrits

I thought my light grey grout was supposed to stay light grey.. not turn black?