To answer the original question it seems as tho the plants are just super stressed, and when they get stressed they drop their leaves and fruit to survive. They are getting much different conditions than they were at HD, where they outside or inside a greenhouse in HD? I am going to guess that they were inside or at least shaded, they had to be hardened off in before just putting them in full sun. This is done by SLOWLY introducing them to the sun for a short period of time gradually working up to full day sunlight. Stop fertilizing and watering until you know for sure they are dried out. Than completely soak and repeat the cycle. Citrus will survive slightly dehydrated better than they will flooded. The meter you are using measures the electric conductivity of the soil so if it is littered with fertilizers you will get false readings. Are you able to post pics of the trees and their pots? I would suggest a re-potting and pruning, but as you said you are new to gardening and this may scare you a bit. Do you have any friends with a green thumb that could help you with this? Don't expect any flowers or fruits till next year as said since the plants are so stressed, but you never know with some TLC and luck you may get some winter blooms. Again pics would really help, and good luck!

The first floor grows my beet greens while it heats the floor of the second floor so the citrus have warm 80 F roots. This device was made out of scrape in the basement. My trees tripled in size over the winter. Click on link below to see other lighting setups Here is a link that might be useful: http://s1094.photobucket.com/user/wreristhechimney/slideshow/GROW%20BOX%204%20BY%204%20BY%20X

The sucking of the aphids causes the curling. Regarding the ants, you are fooling yourself; in citrus, if you have aphids, you HAVE ants... look closer and around a 6-8 foot radius. It is a fact that aphids and ants can exist apart; but in citrus in my 60+ years experience, I have NEVER seen aphids without ants.

Thank you, Silica. I will contact the local Extension service. Meanwhile I found this on Citrus Black Spot: https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/citrus/citrus-black-spot/citrus-black-spot . The description of the spots does not quite match what I am seeing and fortunately the fruit has not been affected. My lemon tree started as a volunteer. Its parents may have been commercial citrus cultivars but it grew from a seed spread by the wind or wildlife. I wasn't sure what it was when it first appeared in my garden but it was too close to a rosebush so I put it in a small pot. That was about 10 years ago. I have 2 other store-bought lemon trees but they are more than 40 feet away and so far neither has spotted leaves.