Just a quick one, why is almost every pic I see of an unhealthy plant in a tiny amount of medium? I've always planted straight into 3-5 gallon pots.
It's pretty much 90% of time I see them in tiny pots, they have deficiencies of some type. For a quick reference, within 15 days my plants have rooted down to the bottom of a 300mm deep, 4 gallon pot. It's also very easy for your pH to go stale when using such a small amount of medium.
Transplanting is probably one of the biggest causes of growth stagnation, and I see it all the time. Gets transplanted, stunts.
I can 100% tell you that my roots would be twice as deep as the medium you have provided within a week. Not joking.