QUESTIONI have 4x4 inch white ceramic or porcelain (not sure which it is) tile in my shower stall and very hard water that makes it difficult to keep clean. The rest of the bathroom is 1950s pink tile (walls and ceiling), but the white tile in the shower stall looks like it was put in later to replace some of the older pink tile. When I first moved in about 15 years ago, a few of the white tiles had a strange purple stain on them that I thought might be the result of past mold problems or damage from cleaning products. The purple color is ingrained in the tile and will not come off no matter what I try to clean it with. Now the problem seems to be spreading to other tiles, and the other day I noticed that the stain follows the exact same patterns across several different tiles. For example, one tile has a group of blotchy dots in the left hand corner, then a couple of vertical streaks, followed by more dots and smudges across the top of the tile. The tile next to that one has the exact same stain, and a few tiles away there is another tile with that pattern as well. It's like some kind of chemical reaction is going on in these mass produced tiles. None of the pink tiles in the bathroom have this problem, just the white ones. Do you have any idea what could be causing this stain and is there any way to clean or restore these tiles?
ANSWERANSWER - Since you don't see the purple stain in the pink tile, but you see it in the white tile, and you can't clean it, it sounds like you have a microbial staining or mineral staining showing through the white tile.
Although it is not common, some glazed wall tiles are somewhat translucent and porous. The tile glaze is translucent so when the underlying tile clay body gets wet or stains it shows through the surface glaze.
There is a chance that the pink tile has the same condition, but the pink glaze is opaque so you can't see the underlying staining.
There could be a purple color microbial growth developing in the tile body that shows through, or it could be mineral staining. Purple Cyanurate is a chemical/mineral imbalance problem, and is not an "organism" or algae problem.
Normally if you have a staining problem, it means you have a moisture problem. Moisture is likely trapped behind the wall and there is some sort of organic food so that a microbial growth develops that will stain the tile. Or it is a mineral imbalance that causes the staining.
To dry to remediate the problem you have to treat the problem, which is excessive moisture, and not the system, which is the stain. If moisture is the problem then you have to stop the excessive moisture, which you might be able to do without tearing the whole shower out, or you might have to replace the shower Stopping the moisture might not allow you to remove the stain because it may be trapped in the tile itself.