With ammonia remover in the tank, the new filter would have been able to take over immediately, as it is a chemical media that will have outcometed the existing bacteria colonie over the last few weeks, killing all benificial bacteria in your tank due to lack of food. Great you might now be thinking, I'll go turn off the old filter now.
Sorry, but that bubble is about to be burst. Your tank is now reliant on this media, and when it is saturated with ammonia, you will get an ammonia spike that could potential wipe the tank
Also, when medicating, this media has to be removed, as it will interfere with treatment
In both situations, you will be left with filtration that cannot cope with the bio-load
Where does this leave you
In short, in a very bad situation
I assume the LFS sold you this media, as from what I remember it is not supplied with this filter
You need to remove this media from the new filter, then if you want to avoid a mini-cycle later, you also want to remove the old filter at this point also. Now you need to fish-in cycle the tank from scratch
With luck, some of the old bacteria will still be presant, and this will only be a large mini-cycle that is over in a few days time
Failing that, you are likely to have 4 weeks of realy had work ahead.
Take a look at [topic="224306"]this thread[/topic] for details on how to fish-in cycle. The good news is that with regular replacement you can put off the cycle untill you are ready, by keeping the media in untill you are ready. The longer you keep the media in though, the longer it will take to cycle the tank. Double edged sward so to speak
All the best of luck sorting this
Rabbut
Edit to add; Just seen you other post. Another box of biomax would have been the better option I'm afraid