Ahh. What's happening?

I am in week 4 of veg in my 3x2 micro garden using fluorescent 4000k T5s. The plants are soil mix of 30% mushroom compost and 70% potting soil. The tips of the fan leaves closest to the bottom of the plants started turning yellow then brown from the tips inward and died. it has slowly moved its way up the plant. The new growth of the main colas and the new growth from the lower nodes are Lush and green. What is happening to the fan leaves?

Sounds like phos def. Its been happening a lot in this section lately. A guano tea will remedy it.

I actually watered for the last two days with botanicare veg nutes. I'm pretty sure it's organic an contains both worm, bat, and various other seaweeds and things. They seem to have started to look a lot better in my opinion. I just wasn't sure that would remedy it so I decided to post. Thanks a lot bro!