so ive just taken delivery of my new filter as my stingray one is rubbish, will it be better to stuff my current media in with the new filter and remove the old or run both at the same time for a week or so?
Cut down and fit your old media into the new filter. Keep as much of the new media as possible but the old media is more important!
If you run them both together a month might not be enough. The bacteria will only move to the new media if it needs to and if you don't add any new fish then the bacteria in the old media will just stay there and none will need to grow on the new media. You'd have to run them together for a very long time to be sure of getting the new media colonised.