Hey people,
so I was cleaning my husband's shower using some 'biodegradable' cleaner and sure enough it bio-degraded his tile

It shows as the stains on the tile that are much lighter than the tile itself. I have one of those beigy stone looking tile that seems like it is ceramic in reality.
So I tried to take the stain out by brushing the tile down and it seems to be working but I am afraid of screwing with the top layer and possibly getting something uglier than the stain, like mold or something.
Does anyone have any advice for me?
Thx.
Sanja