Can I Run 2 Filters In Line?

Hi All- sorry if this has been asked somewhere else! I have a 200 litre, running fine with an  eheim 2217 underneath. A few months ago, I won another one with a joke bid on an auction site. I originally set them up to run together, but eventually took out the newer one as there was too much flow and plumbing in the tank
(not even mentioning the cost and the maintenance). My question is could I run the newer one as a 'dummy' filter, running off the original with one of the pipe size adaptors that eheim sell? My plan would be to fill it with more bio filtration. I cant see any issues with doing it, as the eheims are simple canisters, but does anyone know why I cant? Thanks very much in advance.

Yes- you're quite right Simon- I remember seeing those. I suppose it might slow the flow a bit, but that's not an issue in such a reasonably sized tank. I also need to use the watertight connectors between them so that I can take them out one at a time.  Other than that, I think its going to be a great way to use all the spare media I've built up over time. I'm going to give it a go next weekend. Thanks again.