New filter

Hi all - I've been lurking here for a while and enjoyed reading the posts.

I'm sure someone here can help me out with a bit of advise so here go's ...

I've just installed a Rena Filstar xP3 external canister filter on my 55Gal
Oscar tank. (3 in there at the moment and growing nicely - good job I've got
room for a 300Gal!).

At the moment I'm still running a Fluval 4+ filter too.

My question is, if I take the filter media out of the 4+ and put it into the
xP3 (It should fit with a bit of minor cutting and shaping) - can I remove
the 4+ and expect the level of biological filtration to remain good while
the BioChem Stars grow their own bacteria culture, or should I run the two
filters side by side for a while (How long is recommended?) until the xP3 is
'matured'?

Thanks in advance!

--
Eddy