Eheim Substrat

Hi All,

I have a couple of Eheim Professionel 2s that have been using the same
Substrat media since the filters were purchased (one two years ago, one
about a year ago). From what I've read, it seems like this media was
designed to be changed on a regular basis. Why? Does it lose effectiveness
after a while? I rinse all the media in the filters about once a month when
I do water changes, and it seems to be clean after the rinse is complete.
If I am supposed to change it once in a while, about how often should I
change it (I know it most likely would depend on the bioload of the tank,
but I'm looking for a general guideline)?

I see that Eheim now makes a new version called Substrat Pro. Do people
have any comments or opinions on this new media? I'm debating whether to
try this new stuff or keep using the regular Substrat.

Thanks!
-Peter