A look at the leaves

The soil

The leaves fell off when I touched the new growth.

a pic of a leaf

Congratulations, that's a beautiful tree! :)

The second to the last picture (where you're showing the new growth) looks almost like scarring from citrus leaf miners. Look up pictures of CLM and see if it matches anything you see on the tree. Could be old, too, in which case, I wouldn't worry about it.

New growth tends to be lighter in color but it looks almost like magnesium deficiency due to the christmas tree pattern. If you do decide to add magnesium, also consider adding calcium as they come as a pair and too much of one prevents the tree from using the other one. Try to get a good fertilizer with magnesium and calcium in addition to a good NPK ratio. I believe that everyone likes Dyna Gro here.

The speckling on your leaves could also have come from spider mites. They look like tiny dark or red pinpoints that move. See anything like that on your tree?

I'm still in the process of trying 511 myself but I've heard nothing but good things about it. It almost doesn't matter how damp or wet the soil is right after you water it. What matters the most is how fast the soil dries out. Its okay to be damp right after watering. If you use a water probe, wait until its just below 50% (debatable for all the experts out there, and I'm no expert) before watering. You should have to wait no longer than a week for your soil to need another thorough watering (in my opinion).

I have no guesses as to what the tiny white bugs in your soil are but I googled springtail and the pictures that came up are simply horrifying. Good luck!

Thank you so much for responding Marme! I'm still waiting for the soil to dry out some more. I haven't watered the tree since it first came. I've been using a pencil to test the moisture in the soil and the top is finally drying out but still moist underneath.

I've been trying to gather stuff for the gritty mix instead of 511 after doing some more research and I'm just waiting for everything else to be delivered so that I can start sifting through my materials :)

I contacted lemoncitrustree.com about the bugs and they are sending another tree because they think it might be fungus gnats. I still think it's springtails because there aren't any bugs flying around the tree. Either way, they are not a big deal and they're not going to kill the tree and now I'm going to have 2 meyer lemon trees. I hope this all works out!

In my experience, fungus gnats seem to really like soil with more peat or compost, so the gritty mix will probably help take care of that problem. I've also not seen spring tails in grittier soil either. Never saw either in a proper cactus mix. So changing them over can only be good.

Very cool customer service there, to send a replacement right out like that, nice!

OOo, fungus gnats I have experience with. You would definitely be able to see them. You may not be able to take a good picture but you should be able to see. They look like fruit flies but don't respond to the vinegar and soap mixture. What I do for fungus gnats is to repot and wash the entire plant in a soapy mixture (get rid of the eggs) OR during the winter, I let the soil dry out almost completely, until the plant almost wilts. The fungus gnats can't survive or procreate in such dryness. The only downside is if the plant gets so weak and it gets so dry, then you have to worry about spider mites. :/ for us citrus people, it will always be a constant battle. :)