mildew in a travertine shower

Last summer (July 2006) we replaced our shower with a tile shower. We used something called "Creme Limestone": http://www.mlwstone.com/productdetails/default.aspx?prodID=449&cat=108 I was told that, although it was called "Creme Limestone," it is actually travertine. It has a "tumbled" surface. After installation, we sealed it with Aqua Mix Sealer's Choice Gold: http://www.aquamix.com/for_home_use/products/pg_detail.asp?pdid=3453&pgid=37155 We are having a problem with black mildew stains that appear to occur mainly on the grout, both between the tiles and also on the grout that fills the many natural holes in the stone. We have been attempting to clean the mildew using Aqua Mix Stone Cleaner, but it requires extremely vigorous and repetitive scrubbing. It seems impossible to completely remove the mildew, and then it comes back again in a week or two. We also have a problem with a pink coloration coming from minerals in our water, which is not as big of a deal, as it comes off much easier than the mildew. My wife thinks we need to strip and reseal the tiles and grout. My question is: Do you think that MB-9 Mildew Stain Remover will solve our problem, or do you think that stripping and resealing would also be helpful in minimizing mildew stains? If so, can you recommend specific stripping and resealing products? Do you think an inadequate initial sealing could be allowing the mildew to grow in the grout more easily? I look forward to your response. Thank you, Jim