Altum wrote,
There's nothing magic about foam. Bacteria will grow on any tank
surface exposed to ammonia/nitrite and oxygen. Give it time...

If I understand it right, the filter came with a mesh bag - not a
bio-bag, or foam insert. Without enough bio-media, I can see a filter
that may not be able to keep up with the fish load - if that's the
case, a little foam would indeed be "magic" ;-) ............... Frank