Hey Kal!
Well my girlfriends tank had been going for a good 2 months with that filter in now so the bacterial colony + donated mature media was quite large (large enough a small portion wouldn't harm it). I had placed the ceramics in her filter for about a week, now I have removed the ceramics I placed in with noticeable bacteria gunk on and took a small snippet of the mature media. Placed the cermaics and mature filter wool into my filter and have it running and starting a fishless cycle. I'm hoping that even a snippet as small as I took will be enough to "seed".
It's turned out good for my girlfriend though she got 0.0 on her readings! So I add more ceramic media into her filter to keep permanently,I was modifying my stingray 15 to take ceramic so I had more than I needed! Also I think my stingray is a little too big for my 38litre tank haha. I'm building a planted betta tank you see!
Edit: Also her Poly/Carbon inserts seem to house a hell of a lot of bacteria!