It usually depends on the brand of sand filter systems.. Do you know, Waterco only use 2 layers of Zeolite for their POEs? Other filters may have 6-7 different layers of media in their system but still results higher than 10 microns of filtration quality.

In my opinion, it doesn't matter how many layers of media they use. What's important is the type of media.
Sand filters consists of a few layers of GRADED silica sands and anthracite as filtration agent, activated carbon for chlorine removal is however, an option.