The safest thing to do is run it in conjunction with the existing filter for a month. The other option would be to move all of the bio media from the old filter to the new one. What is your fish and plant load like?
+1 to the media transfer and rock on.
when i went to my sump, i didnt move a single piece of media and there was ammonia for maybe a day?
lots of bacteria reside on everything. and when it sees an opportunity to grow. it will.