Mike, good idea to post symptoms here, but since it is a citrus forum, I should point out that in many cases, the symptoms you've listed don't occur on citrus, and that the actual symptoms on citrus are quite different from those listed. For example: Calcium -- seldom visible symptoms on citrus Magnesium -- never symptoms on new growth of citrus; old growth shows a characteristic "inverted V" of green at the base of the leaf and yellow-orange above. Phosphorus -- I've never seen a citrus tree exhibit the purpling of leaves; rather, reduced fruit size and yield is most common. Boron -- in citrus, shows up as dead, sunken, gray or brown areas in the albedo (white part) of the fruit peel. Usually no other symptoms. Copper -- Growth may be unusually vigorous, producing huge, deep blue-green leaves, but the stems are too weak to support the weight, so they bow unusually, giving what is known as an "S" shape to the limb. Also, such limbs develop blisters on the epidermis which swell, then burst open, and ooze a sticky sap. Then in areas of the world that have fire ants (e.g., Florida), the ants are attracted to the sap, and they chew away the epidermis, killing the twigs entirely. Manganese -- at least in Florida, even a fairly severe deficiency generally has no effect on yield. Molybdenum -- older leaves are green with large (up to 1/4") yellow spots, like large freckles.

no evergreen .. holds its leaves forever ... but i cant tell from your pix.. if this is the oldest leaves.... how do the fresh new leaves look.. at the growth points ??? why indoors??? ... lights need to be about 2 inches above a plant ... for requisite light levels.. and the problem with a plant as large as yours.. is its shear size.. and how a lamp near the top.. will most likely do nothing for the leaves below .. hence.. it might be shedding them ... and this is why plants this size.. are usually .. put outside for summer ... there arent many houseplants.. that have many big flowers .. and that is because of the energy it takes.. to generate many big flowers ... and if your lights are not giving the plant enough light.. then something has to give.. and its usually the oldest leaves ... you can not make up low light levels.. thru fertilization ... ken

Very often nutritional deficiencies are due to the roots being unable to take up the necessary nutrients even though the nutrients are present in the soil. This may be the result of alkaline pH, root rot, lack of oxygen at the roots or improper temperature. I can't tell for sure, but it looks looks like your soil may retain too much water, not allowing enough oxygen at the roots and possibly causing root rot.

Others on this forum have had good success with neem oil, although I've never used it personally. I have been battling a spider mite outbreak on my indoor citrus. Two products that I find work well are: Safer's insecticidal soap and Monterey horticultural oil. Any oil or soap must directly contact the mites (and their eggs) to be effective, so excellent coverage on the top and bottom of the leaves is required. https://www.amazon.com/Monteray-6290-MONTEREY-HORTICULTURAL-CONCENTRATE/dp/B001RPVUCY/ref=sr_1_2?ie=UTF8&qid=1495043455&sr=8-2&keywords=horticultural+oil https://www.amazon.com/Safer-Brand-5118-Insect-Killing/dp/B00192AO90/ref=sr_1_2?s=lawn-garden&ie=UTF8&qid=1495043593&sr=1-2&keywords=insecticidal+soap