here is a great site for learning about difiencies in citrus. fertilizers, minors. Its a great site to really really read carefully through. You'll learn a lot

http://www.flyingdragoncitrusnursery.com/deficiency/index.htm

sorry, forgot to add the link

heres another

http://edis.ifas.ufl.edu/CH142

http://www.agric.nsw.gov.au/reader/citrus