Nutrient deficiency or growing medium problem?? Photos attached. The older leaves on my young citrus trees (Gold Nugget and Nova Mandarin and Ponderosa Lemon) all have a mottling of green and white/light yellow. New growth is the usual green until they mature...then they change too. The trees are planted in 1 gal. plastic posts with good drainage in medium size coconut husk chips only - no soil. I use a concentrated liquid citrus fertilizer 5.1-2.5-3.7 diluted in a bucket. I sumberge the whole pot in the bucket until air bubbles stop and then allow to drain. Also have used a slow release 30-10-10? which I am out of. Do you know what is causing the leaf discoloration? Does my planting medium suffice? Thanks for your advice!