I repotted it on day 15 but unfortunately I damaged the roots a bit. It still seems to be recovering from this because its growth has slowed down considerably.
I have now turned the light up to 50% and started fertilizing. I'm using the Guanokalong fertilizer formula and Piranha from Advanced Nutrients. I will give Piranha for the first two weeks after each repotting and otherwise stick completely to the Guanokalong scheme.
Also started with some LST. Will perform HST as soon as the plant is 2-3cm bigger.