never replace all of your filter media at the same time, and you should just rinse the media inserts in old tank water to clean them, every once and a while you will need to replace an insert, i think its every 3 months(i could be wrong)
but again never replace it all with new stuff at the same time. try to alternate, one month replace the bio chem, next month replace the ammonia, this will ensure that you still have a proper ammount of BB