Reading here and there and other places the eheim biosubstrate does have a reputation of clogging. So I am in the process of replacing them with ceramic rings. Flow and performance is better. 
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could you provide some links to this? 
first there is no such thing a Ehem BioSebstrate (and no Eheim media is "glass balls").
Eheim make Ehfisubstrate and Ehfisubstrate pro. neither is known to clog, put substrate pro, suffers less. i also need to point out, you have little or no Bio filtration. if you use Eheim Ehfimech rings. they have no, significant bio action. indeed they are not porous in any way. perhaps visiting the Eheim site? you will know, at least, just what Ehem sell and make.
as for if their filters come with media? well NO, but also yes. it depends on the deal the shop is offering. but Eheim state, under normal circumstances, no media is shipped with their pro cannisters.