The use of pre-filters is important in prolonging the life of the (expensive) high pressure pump in your watermaker. Regular replacement of pre-filters is recommended. See your manual for specifics.
Sediment pre-filters are pleated and rated in microns, according to the size of the particles filtered - the smaller the number, the finer the filter. Typically, 5 microns is standard, but for water with a high concentration of particulates, a 20 micron filter or 75 micron plankton filter may be installed before the 5 micron filter to prevent it from clogging prematurely
Carbon filters have no particle size rating, and are used to remove tastes and odors; carbon filters are white, and are not pleated
Plankton pre-filters are also pleated and are rated at 75 microns. They are used when the seawater has a high concentration of larger particles - often this occurs during algal or plankton blooms
Pre-Filter Housing Wrench makes opening the filter housing much easier
Use 2-1/2" pre-filters with Clearwater 400/600/800; Island Explorer 500/900
Use 4-1/2" pre-filters with Claerwater 1200/1500; Island Explorer 1200; all Work Boat