Leaf Curling and yellowing on three week old plant, how to stop this gettign worse?

Hello my friend, the light is too strong for this young plant. Move the light up or the intensity down!

What's your pH?? In coco you wnt to be around 5.8 or so.

Normally when the leaves taco its from to much heat and or light. I think your solution of raising the light up is a good start, on your nutrients, manufactures tend to say use x amount when its a bit much, this makes you buy more. I find it best to mix the nutrients into the solution at the ratio they advertise, and then dilute down to the desired EC. If you don’t have a EC pen might want to look into getting one. If you cant lower your heat, realize the plants will drink more water and suck in more nutrients the higher the temps and with lowish rh. This means your feeds need to be less concentrated to off set the increased thirst of the plant or they will burn. Good Luck!