this is my first time growing.so theres not much i know so i ordered some seeds from online. and i planted them they been in vegg. for 3 weeks now. some are almost 2 feet tall. do i start to flower and switch to 12/12 light?? also theyvare turning yellow and have brown spots. what do i do? i have been using a 600watt hps light is that fine.?? any tips??