Size of particles filtered: 2-5 microns.
Whenever the pressure reaches 10 psi or higher than starting pressure. Usually depends on filter size,bather load, water condition and pool environment.
After each backwash must add DE (usually by adding in pool skimmer)
Fast, provides the finest filtration of the three media,if used with multiport provides flexibility of sand filter, needs to be backwashed less often.
Cons: More expensive, must replace DE after cleaning, use of certain chemicals may clogg filter faster.