I'm guessing its just a response to the cold soil temperatures we had this winter. When soils are cool, plants (especially citrus) have a hard time pulling nutrients out of the soil. When the weather warms up the symptoms usually dissapear. This is one reason why it isn't beneficial to fertilize in the winter - plant roots are pretty inactive at this time of year and can't process the nutrients. As long as you followed the recommended amounts when applying your fertilizer your tree should be fine. In case you need more information on fertilizing, use the U of A publication located at the link below. A guide to common nutrient deficiencies and herbicide damage can be found at http://cals.arizona.edu/pubs/crops/az1007/contents.html Here is a link that might be useful: Fertilizing citrus

Just to let you know again, spider mites can't be seen by your normal eyesight. They're microscopic! University of Florida describes them as 1/50th inch long. The female is 0.4 millimeters. You can't "see" spider mites, literally! But just because you cannot see them with your plain eyeballs, doesn't mean it's not on your plant. Your leaves show the most common spider mite symptom. I would advise you not to ignore the very high likelihood of spider mites on your plant. Your organocide will only kill adult bugs on contact but any eggs that are on your plant will not be affected. You'll have to keep spraying until you take down every last bug going through their adult phase

A photo would really help. Words alone can mean very different things to different folks, But based on the info so far I'd be questioning the magnesium and the azomite additions. Such additions are unusual unless based on a professional soil test and could easily create problems. Dave

Are you sure it isn't too wet? I can't see the soil but the plants look pretty sick. Did they go through a cold morning or more? The one leaf looks burned from something - too cold or too hot? Lift the root ball out and see how wet the soil is. If very wet put the root ball on some newspapers to wick away a lot of the water. After a day or more, put it back in the pot if you want it in that pot and that soil. You might be further ahead by pulling out the begonias and check the roots for rot. If not rotted, put them into a smaller pot with fresh potting mix. Do not over-water until they are actively growing again. If rotted you can start some new plants by cutting the cane above the rot and rooting them in water or a good potting mix. DO NOT OVER WATER though.