How far is your lamp? It might be too close; I keep LEDs at 35-40cm and HPS at 60cm away.
If you're already using nutrients, then leave them out for now except for root extract, and I would only take half the recommended amount and water no more than 100-200ml per day. Draw a circle with water around the plant about 5cm away from the stem; this forces it to search for and stretch its roots. But the most important thing is not to overwater; they don't need that much. Until the first side branches come, almost 200ml a day is enough.