After seeing how the Mango Whisperers are able to diagnose nutritional problems I started looking around the net. There are many sites that help you do this, but this seems to be one of the better ones, the flow charts are great, and learning about mobile and immobile nutrients was the real a-ha moment for me.
http://landresources.montana.edu/NM/Modules/Module9.pdfIt was designed for grain crops (I don't think they grow many tropicals in Montana). I think that the core symptoms should apply to most any plant. It doesn't cover pH lockout and many nutrient toxicities but it is still good. Multiple deficiencies can really muddy the water.
It does seem like the easiest solution is to fertilize with major-minors-micros for most nutrient problems (defiencies at least).
I've been Fe and Mn dosing a couple of plant after reading this, I think I am have some success.