Were it me,I would not fret over pH and nitrAtes at this point. I would submit that the fact fish are still alive,is a sign you are doing things right. Keep an eye on ammonia and nitrites and change water when needed to keep levels as close to zero as you can. The Nitrates will appear ,they have to unless you do something to interrupt the maturing process(cycling).
Leave the new filter and the old one run together for another couple weeks and the bacteria(good kind) will begin to develop there as well as the old filter. A good dechlorinator such as PRIME in case I haven't mentioned it ,will also be very helpful for new water you add during water changes. Hang in there.
Don't overfeed,don't disturb the filter material pads,sponges,cartridges,etc and if you don't overfeed,then vaccuming the gravel can wait until the tank has cycled. Then all you gotta do is once weekly water change and maybe vaccum one half the tank and the other half the next week and so on.
Sometimes we get too caught up in testing although it is necessary with fish in the tank ,but the only thing to really worry bout is the ammonia and nitrites . The rest takes care of itself. Is frustratingly slow process sometimes but by not over feeding ,performing water changes to keep ammonia and nitrites in check, it will happen.