New Aquarium question

Over the past week, I have set up a new 200L tank.

Everything in the new tank is new, except that I re-used my Eheim
cannister filter. Because of an algae problem in the previous aquarium,
I cleaned the filter with vineger, and it contents by leaving them in
the sun for a couple of days.

I used a "Cycle" bacteria water treatment on filtered tap water, and let
it stand for a day unfiltered, then ran the filter for a couple of days
before starting to add some cheap and hardy fish.

The tank is well planted, and I have fertilised the plants.

After a week I have 10 small fish in the tank, which I have added
progressively over several days, whilst testing Ammonia, Nitrites and PH.

I have not yet detected any Ammonia or Nitrites, but today the PH is up
to 7.2 - 7.4.

Everything that I have read says that I should be measuring Ammonia by
now. There can only be two reasons that I can think of why I am not:

1. There is enough bacteria from the filter and treatment to make the
tank stable already.

2. The ammonia cycle hasn't yet started.

How do I tell which? What does the PH change mean?

Thanks

Happy new year to you all!