im in no way an expert at any of this but I dont think its calcium, maybe a Downy mildew, check underside of the leaf see if you see a if you see a fuzzy or fungus growth
Keep an eye out for white flies, though I don't see any there.  now(wet season here in FL) is the time for bacterial leaf spot to show up, I just treated all my plants with a Neem, soap, H202 and Epsom salt mix cause I found some leaf spot on a couple plants. Â
 http://www.using-hydrogen-peroxide.com/peroxide-garden.html