Humm...I think you may be right, I was at the garden center a few weeks ago and my citruses actually looked better than theirs. Since then I've brought them inside and they've lost some leaves due to the adjustment. Plus my existing citruses have buggie issues (scale, aphids, and mites) which I treat with cotton swab treated with alcohol as well as occasional Neem sprays. When they came indoors the bugs went nuts so I've done a major cleaning but there has been some leaf drop. They are covered with blossoms though. They are also kept away from the plant for my brother. Your comments about the different feeding probably explains the Key Lime being smaller than the Meyer. I figure I'll do the transplant and hold onto it until it's ready to move. My brother's place will have a nice sun room, no bug infected neighbors, and he's local so I can/will provide any major care. I just wish I could get rid of the bugs once and for all. They came with an ornamental tree I took over from a friend who moved over 8 years ago. Alcohol is my friend...

The fanciest I get is following the recommendation of some, combining a cool white tube with a warm white tube in those dual-light fixtures. Helps in getting wide range of light (blue to red ends of the spectrum). Good luck!

It could be that your citrus isn't getting enough sunshine...they like a LOT of sun! I have 2 orange trees and a Meyer's lemon planted out in my yard here in Shreveport, Louisiana (zone 8) and they do EXCELLENT! Despite what many people think, oranges CAN handle a freeze...as long as temps aren't TOO low and don't last too long. I planted my trees 8 years ago, and now they are huge and healthy and VERY productive and we do get freezes from time to time here. You might also want to check and see if they are root-bound. My citrus grew very fast, so it could be that yours have outgrown their containers. If it helps, my trees are, one Valencia and one Louisiana Sweet and one Meyer's lemon.

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!