HELP .. Grout Haze

I'm working on repairing the grout in a shower .. and am wondering if there is a trick to getting rid of the grout haze that appears on the tiles. I've tried to be diligent about wiping down the tiles with a barely damp sponge .. then have gone over it with a clean, dry tile rag .. apparently specially designed for polishing tiles and removing grout haze .. but I'm having a really tough time.

Am I just too impatient .. or is there some trick that I'm missing????

Here's a website with some info
Grout Haze

I use a wet sponge and bucket of cool water. Just keep rinsing the sponge. You will have to do this two or three times.