The bleach pens are made mild so you can use them on fabric and they either work or you walk around with a spot on your shirt. I suspect they are just diluted dry cleaning fluid in a pen? I really doubt they are bleach or by now a lot of people would be suing that their favorite garment had bleach spots on it. Because it sort of worked, try plain ole dry cleaning fluid. Wet a paper towel with it, stick the paper towel up there making sure it has full contact with the grout and walk away to let it sit. Maybe save money, try the paper towel trick with bleach or a cleaner you already have that made a difference. All the saturated paper towel does is stick there and it lets the cleaner have time to actually work instead of immediatly running down the wall right after you spray it.

Somewhat late replying, but thanks very much for the suggestions. Oh and I have tried every cleaning supply in the house. I will try the baking soda, but do believe the poultice might be a good solution.

Thanks for your messages. When I read Home Forum, "Cleaning Tips" a thread on mildew in caulk no travetine was involved. It seems that peroxide or tea tree oil will kill mildew spores, but clorine bleach is needed to remove the stain. I was concerned these materials might damage the travertine, however seeing that buddysmom has used Oxyclean & other places on the web has also, I'll try that. It appears that Clorine bleach is Alkaline with a PH of 12 to 14 (Vinegar = 1) that I/we might be ok to remove the stain with a dilution of clorine bleach & water. My stain is primarily on the grout (with some in those small pores -- my contractor actually scraped the grout across the travertine to attempt to fill many of those & allow it to still look natural -- of course that grout possibly washed away 1st :-(). It sounds like alkaline on travertine is ok, but I'll dilute & not leave on too long. Thanks live_wire_oak. I will probably make a different decision next time on travertine in the shower, but I had such good intentions & it is so very attractive . . . I'll let you know how it goes.

I use chlorine bleach exclusively and never had a problem. If your claims of dingy towels after use are true, you got something else going on. Percarbonate while an oxidizer, will not outperform LCB as a stain remover. My suspicion is you used too much. 4 rinses is substantial to have lingering effects. All LCB is not the same just as detergent. My question is why are your towels dingy anyway if you have been a user of percarbonate? Dingy clothes are caused by redeposition of soils not remaining in suspension during the wash process, or too low of temperature. Everybody has a preference, but LCB always has a place in the kitchen, bathroom, and laundry room. It is the gold standard for disinfection!