The last year or so I was using Epsoma Citrus Tone to fertilize all my in ground citrus, feeding generally Feb - Aug every 6 weeks or so. This spring I switched to a locally blended commercial fruit tree mix 18-9-11, which is much cheaper than the Epsoma Citrus Tone. Also last year I did scatter some Azomite around all my fruit trees for the micro nutrients, and last year I added Epsom Salts around all my citrus, as my soil generally is extremely deficient in Magnesium, again same amount around the other younger citrus. Soil testing this spring from the citrus area, still shows levels of Magnesium on the low side. I have my citrus trees planted on a 25-30 foot spacing, arcing outward from my older mature citrus / fig tree, so root competition should not be a factor, also I have 3 other citrus trees planted about the same time on this arc (the one with the issue is 2nd from the end of the arc).