I will tell you what I have learned from some of the experts in South Florida. Apparently high phosphorus in fertilizer tends to bind up trace elements such as magnesium, making it difficult for the plants to absorb these needed nutrients. So it is recommended to give magnesium sulfate (epsom salts, sold cheaply at pharmacies) at 1 tablespoon per gallon either alone, or mixed with a phosphorus-free fertilizer such as 10-0-10. You can do this monthly, or twice monthly, between fertilizings. Hopefully others can chime in with more info for you!