There is some stuff out there called Kills. Its in the paint section of Wal-Mart, Home Depot, Lows ext. You would have to tape and paint the grout but it will kill the fungus that keeps comming back. It does the same thing on outside trim on a house. You can paint over it and it will keep comming back. Kills is the only product that kills the fungus. Randy
The stain on the tiles is fungus and it will continue to return until you use something that kills the fungus
I use to own and operate AB Tri-State Termite & Pest control, Inc. I sure could have put both of you to work!! Good Job!!