everything goes well up to 3 to 4 weeks and then it starts to act up?
you just need to gain experience, by doing it over and over and over, and many more overs.
I still "mess up" a run here and there, but honestly that's just ego because the plants don't look as nice anymore.
I fertilized my last grow in this phase and it only got worse.
pH: 6.2
Tap water: EC 0.4
that's too little, just for the size alone I can tell
the soil is giving out now, the yellow is a starting nitrogen deficiency, but don't worry let them just eat the lower leafs. Now start feeding at constant EC of 1,2 at about 2-3-4 NPK ratio.
also pure tap water often messes with the soil availability, even when pHd
the small pot sizes usually need the same food EC as the soil EC, throughout.
they look a bit drought/over water cycled too, this you will just learn to avoid over time.
experimenting with pot sizes, watering techniques, blabla etc.
also adding exact flowering days to your posts, would really help the whole remote diagnosis thing...
early starving, but overall still looking great
whats your fertilizer gonna be?