Talk:Media filter

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You have your information wrong. A multi media filter operates on the principle that the media is stratified based on media density, not media particle size. The lightest media; typically the anthracite, is the most course (largest) of the media. Being the least dense (lightest) it settles out last, thus it will settle out after a backwash as the upper most layer. The sand (typically a graded quartz sand) is next to settle; it is more dense than the anthracite but less dense than the garnet and has a smaller particle size than the anthracite but larger than the garnet. Finally, the most dense and smallest in particle size is the garnet. It settles out first and will become the last layer the water will travel through with type flow from top to bottom in a multi-media filter. The garnet will produce the finest filtration in a MMF and can be considered a polisher. The layers from top to bottom (graded from particle size from biggest to smallest) are antharcite, sand, garnet. Hope this helps someone trying to undestand the basics of MMF. If they were to read this Wilipedia entry, they would have it all wrong and would miss the true benefit of a MMF as compared to a typical sand filter, that is full bed filtration. Sand filters rely on the very top of the sand bed as filtration.