Do you know the pH of the water you're using? Google "pH marijuana range" and read the first few hits if this is something you haven't looked into yet. The cheapest way to at least get a rough idea of your pH is probably with an aquarium or pond kit. Make sure to buy a fresh kit, not one that's been sitting on a shelf for months. The reagents only last a couple of years.
What's your medium? It looks like soil. Is it a "time-release" product? If so you need to get it out of that stuff. At least plant it into a much bigger container with Fox Farms Ocean Forest or other approved medium.
MOBILE VS. IMMOBILE - From your pictures, I'd say you have one or more mobile element deficiencies. Study up on "mobile" deficiencies vs. "immobile". Google "mobile immobile marijuana problems" to get started.
Here's one site that talks about mobile vs. immobile
http://www.greenmanspage.com/plant_abuse/#MOBILE_ELEMENTS
Take a look at the pictures for potassium and esp. magnesium.
In a nutshell, some of the elements your plant needs are mobile. The plant can literally remove mobile elements from one part of the plant and move them elsewhere. Note that potassium and magnesium are both mobile. If a plant isn't getting enough of either, it will retrieve mobile elements from the lower leaves and move them to the tops in an effort to survive.
So, a plant that keeps producing relatively healthy newer leaves while abandoning lower leaves more quickly than one would expect indicates you might have a deficiency with one of the mobile elements.
Immobile elements stay where they landed, so lower leaves can look relatively healthy while newer growth is afflicted with whatever deficiency is developing.
Start with pH
