my plant is a little over 3 weeks old...im growing it in fox farm ocean forest and have grow big, tiger bloom, and big bloom....some of the bottom leaves are turning yellow....should i start adding a small amount of grow big or should i wait until after week 4?
Looks like a nitrogen deficiency to me. Usually that hits the lower older leaves. Generally means nutes in your next watering are in order.
Have you already been feeding it nutes? If it's only three weeks old, and you're already feeding it, there's a possibility it's nute burn. I am no expert, but that would be my concern.