Your light distance is ok, it could even be closer imo (12inches). Ive used 400w before, so I think 12in is a good distance depending on size of grow. I know nothing on those nutrients you use and their dosage so I cannot comment, but pH is a huge deal. When you add nutrients to water, you are lowering the pH of the total solution. I have a 7.3 pH coming out of my tap, and when I add nutes to a batch of water to apply to my plants, it isnt uncommon to see low 5.0 pH levels, which is WAY WAY to acidic. Also, for soil chemistry reasons, if you have too high or too low pH, which I think you have too low pH, nutrient lockout happens. It surely does look like you have nutrient deficiencies, but I cannot tell you which because I dont know.. But you might be changing your soils pH as you feed your plant over time, which is how lockout of nutrients happens. So if you continue to add nutes, you build up acid levels in the soil and will kill the plant. Also, a really good way of telling this is to check the pH 'runoff' . The water that drains out of your soil. This will tell you what your soil pH is approx... For soil it should be like 6.6-7.0 imo... I know you dont have a way to check pH levels, but I highly suggest you get pH test strips or even better a digital meter that checks it.