I have the same problem in my Mexican Beach House. But, I also have saltillo on my outdoor patio in DelMar. The tiles I have in my patio were sealed when laid. Then each summer or every other summer I scrub them with detergent and a stiff brush.
But the tile in the Mexican house is very, very dark. I think it may have been sealed with linseed oil, which was the old accepted method. So I plan to use detergent and chlorox with a scrub brush. Then I will follow with a degreaser that is strong. When everything is rinsed and dried then I'll use 2 coats of sealant, such as 115 or it's equal.