Based on the Sieve Analysis results for filter media given below:

$\backslash$table$[[$Size of Opening $(mm),$Cumulative Mass $\%$ Passing$],[0\mathrm{.}105,0\mathrm{.}2],[0\mathrm{.}149,0\mathrm{.}9],[0\mathrm{.}210,4\mathrm{.}0],[0\mathrm{.}295,7\mathrm{.}5],[0\mathrm{.}42,10],[0\mathrm{.}59,39\mathrm{.}4],[0\mathrm{.}84,60\mathrm{.}0],[1\mathrm{.}19,74\mathrm{.}4],[1\mathrm{.}68,91\mathrm{.}5],[2\mathrm{.}38,96\mathrm{.}8],[3\mathrm{.}36,99\mathrm{.}0]]$

The effective size is:

$0\mathrm{.}149mm$

$0\mathrm{.}295mm$

$0\mathrm{.}105mm$

$0\mathrm{.}42mm$

$0\mathrm{.}210mm$