The correct sequence for installing filter cartridges is the following:
1) sediment cartridges - remove rust, sand and salt. First the cartridge with high micron rating should be installed, such as: FCPS20, and next cartridge FCPS5,
2) specialty cartridges - softening, iron and heavy metals removing,
3) carbon based cartridges - remove chlorine, some pesticides and organic pollutants,
4) anti-bacterial cartridges - remove bacteria and viruses.