think I posted before to someone else a few weeks ago but I have used Grout Revive by Evo Stik. available at Wilkinsons in a tube. easy to apply although I didn't use the foam applicator, I squirted some of it out of the tube & applied it with a small paint brush. superb results. don't use a grout pen as personally I think they are not much good. bleach is not recommended on some sites as it eats into the grout. this stuff I've mentioned is about �3.20 & worth every penny, believe me! hope this helps