Proper method of introducing a new filter

[KaiserSousay]

I think you are worrying over something that will not be a problem.
You already know your tanks surfaces have bacterial colonies that probably are large enough to cover any filter change you end up doing.
Don`t sweat it, do the change..keep an eye on your water quality after.

 

[CornBread]

Whatever extra filter u get go big and as for the older ones just go to your local fish store and ask for the media material that u have to cut to size to fit in your filters