I agree with crofter and misstyler. I Use Bal without any problems apart from getting my hands clean afterwards!! Also not advisable to use the same sponge on white grout the day after!!
Must say those are some smart looking floors there guys.
lets start a campaign to get black grout banned under the health and safety at work act . its bad for your health because of the stress it causes to tilers ,or at least we could get the name changed to
" black grout fingers crossed " lol