During the Startup phase, plants adapt to the new tank environment. The tank's biological system attempts to find a stable equilibrium. Weak plants may melt, unsightly brown algae might bloom.
Cycling a tank before planting helps. So does providing nutrition from Day 1, and increasing CO2 if available.
For tanks without CO2, this process can be surprisingly long, as growth rates are very slow.
At the heart of the 2Hr Way is understanding the 3 distinct phases of a tank's lifecycle, and the actions at each stage to enable the tank to continue thriving over time.