I started watering with nutrients on day 21, always with the same amount (500ml) with the same frequency, 3-4 days between each watering, depending on how the soil looks. Then on day 22 I switched the LED to 50% of his power at 60cm of the plants. Now they are receiving around 600-670 PPFD. I topped them on the 5th node at the end of week 4.