Black foam in Eheim filter...what is it?

[vugc]

I was given a 6 yr old eheim professional filter,there is a black foam/sponge in one of its compartments.Is that a carbon or charcoal foam or it's just any other foam?Would it be capable of absorbing water column fert?

[loupgarou]

if its fairly thin, its the carbon pad.

[vugc]

It's quite thick and it occupies the entire compartment,so does this mean it's not a carbon pad? It looks more like a sponge actually only that it's black.

[limsteel]

Bio Sponge... very coarse use to cultivate BB... alos remove large debris prior to fine filteration.