density of original filter sponges

Basically, all original sponges by EHEIM for mechanical filtering have a pore density of 30 PPI. 

The inserts for adsorptive filtering (charcoal) have a density of 50 PPI. 

Calculation: 1PPI = 1.3 micrometers / 1.3 micrometers = 0.0013 mm

To ensure that no small shrimp will be sucked in, you should pull a stocking or something similar over the suction of the internal filter, for example.