Growing like weeds

That is most certainly nutrient burn from excess use of nutrients. At this stage in development you don’t need to add any more nutrients to your soil. Just add dress water. The plant is too young and will not absorb the nutrients that you have added to the souls and instead ends up with excess salts that build up around the roots. These salts will dry out the roots and burn your plants leaf tips. Firstly let your pot dry out and then add plain water. Do this until you have a few sets of fan leaves and about 3-4 modes on the plant. Then I would start with a 1/4 feeding of the manufactures recommended dosage. Each week you can up the dose until your in line with the manufactures recomendation or until you start experiencing nute burn again. Use the vegitative phase to help dial in your plants nutrients so that you don’t have this problem in flower. I will be around to keep an eye on your grow. Good luck!