This replacement filter has a special blend of 1/2 sediment filtration vitally necessary for the special carbon blend multi media to perform its tasks/duties to remove unwanted tastes, chemicals, and unwanted particulates. Magic Mountain has custom produced this replacement filter to produce in our opinion the best results possible, for cleanest and best tasting water. Don’t be fooled by other offers our filter is proprietary and one of a kind. This is the replacement cartridge “only” for the L-5551 or L-5651, or the newly engineered M-1000 that came with a new filter head sold recently by Magic Mountain Water Products, “that came with a filter head, filter and mounting bracket, etc” i.e. L-5451 (M-1000) now this is the replacement cartridge for that system as well.