I have black matte finish shower tiles with black grout. I have scrubbed the tiles and grout with a 1:2:1 peroxide:baking soda:dish soap ratio.
Tile and grout cleaned up and all soap scum removed but white residue is left behind on some of the grout areas. All tiles and grout were scrubbed and rinsed twice before drying.
This shower sat unused for multiple years and had been temporarily caulked in places prior to this cleaning. I have noticed there is water under the tiles that seeps up when stepped on as well.
Any ideas what this could be?