I took out the hydrochloric acid and went to work. Here's my before photo:
It took a couple of hours. By then the sun had changed position and it wasn't quite as light as it had been (I wish the difference was SO distinct), but here's my after photo. I can't tell you how relieved my grout is, and how nifty that hydrochloric acid is. Yep - I can cross that project off of my list for the next several years!
