Hard water, soap scum, and etching can all look very similar and thus it may be difficult to immediately diagnose which problem you have. Use the following guidelines to help diagnose the issue and choose the correct product.
Hard water mineral build-up forms a dull, chalky, thin crust on the surface but it can simply look like a dull spot or area. Such spots can form anywhere water has been left to evaporate, but most commonly occur around sinks, faucets, or on shower walls. It's not very common to see random or scattered drops / spots on a countertop from hard water. So, if the spots are not on shower walls or floor or directly around a sink or faucet, you can rule out hard water stains.
Soap scum is a film that forms on the surface from soap residue build-up. This usually occurs over large areas vs. spots. Again, it is only seen around areas of heavy water and soap use (shower, sinks). It is usually smooth but also looks dull and whitish.
Etch marks are dull chalky or cloudy spots that result from corrosion of the surface due to contact with acidic foods or drinks or harsh cleaners. Etch marks are commonly seen as glass rings, spray marks, drips, or spill spots. Typically, the spots are only seen when looking at an angle to the surface and not directly above the spot.
Etching basically eats away the surface exposing more raw marble beneath which looks dull. However, in this case, nothing is "on" the countertop or tile. The surface has been physically damaged.
Diagnosing which problem you have can be tricky. First, if not in a shower or directly around a sink or faucet, then you can almost certainly rule out hard water and/or soap film.
Hard water deposits and soap scum can usually be identified by attempting to scrape off a little of the film with your fingernail or another plastic implement that won't scratch the stone. However, in some cases, the film does not readily scrape off. If you can scrape off a bit, then it is hard water or soap film.
For cleaning purposes, it isn't necessary to determine which you have since both can be cleaned using the Soap Film / Hard Water Remover.
Etching is harder to differentiate. You can perform the scrape test. If you are unable to scrape off any film, then it is likely etching. Or if you applied the Soap Film / Hard Water Remover without any change at all to the dull area, then it is etching and not a hard water or soap film.
Also, etch marks can often look clear or only slightly dull and are often only viewable when looking at an angle to the surface. Hard water deposits and soap films can be seen equally well from any angle.
Etching is repaired much like sanding wood. The damaged surface must be re-finished using this Etch Remover Marble Polish on a shiny "polished" finish or on a matte "honed" surface by following the DIY instructions in the How To Remover Etch Marks ebook.