Here are some common Mohs hardness values -
Sodium carbonate : 1.3
Sodium Bicarbonate : 2.5
Aluminum metal : 2.75
Calcite (CaCO3) : 3.0
Kierserite (MgSO4·H2O) : 3.5
Glazed Ceramic Tile : 5 to 6
Pumice stone : 6
Garnet : 6.5 to 7.5
Glazed Porcelain Tile : 7
Glass (Quartz) : 7
Corundum (Al2O3) : 9
So sodium bicarbonate is often used to strip paint off of aluminum and other metal parts (as well as graffiti off of walls) as it will easily remove paint without scratching the underlying surface. Glass beads will scratch ceramic tile but should be ok against porcelain tile while garnet can easily scratch porcelain. Glass bead blasting is very good for removing calcium deposits on plaster/aggregate surfaces because it's hard enough to do the job and no one will notice a fine scratch in their already rough PebbleTec surface.
So, when getting pool tile cleaned, always ask what materials will be used as you could wind up with calcium free tiles that look terrible. Many tile cleaners will use glass at low pressure to try to minimize scratches and then hide the scratches they do cause by applying a "surface sealer" (claiming that it will keep calcium from reforming, which it will not). The surface sealer is typically just an low weight oil OR a teflon-based sealant that will wash away well after the cleaner has left or, if it's a teflon sealer, will typically yellow over time from UV exposure and look terrible.