I'll be applying two coats of a high-end penetrating sealer to the tiles, and hopefully that will help keep everything looking good. One coat will go on the surface before grouting, and the second coat will be after grouting.
Unfortunately that isn't going to help for long. I've seen it way too many times. There is nothing you can do to stop the leaching of the iron. I installed a big slate patio, finished it just last fall and yesterday I went to take a look at it. Very disappointing!!! That sucker had five or more coats of sealer both before and after grouting and it still looks like hell already.
OH WELL!!! They were warned.
I also have a DIY doctor that did his own slate shower and then later called me to try and stop the leaching. We cleaned and then sealed that sucker over and over and cleaned the stained tub. Now the stains are reappearing and the leaching has begun again.