Thank you for your response hoosierquilt.
A few days after I bought the tree, I repotted it into a bigger pot (about 20% bigger). I was expecting it to be root bound, but the bottom half of the soil fell off without roots in it, and the roots around the side were thin and reddish brown (should have taken a picture). I pulled away some of the soil and some roots came with it, they were very fragile. The soil it was in was very gritty and loose, (sand , perlite, bark chips etc) but also wet and heavy.
I repotted it in a mix of pine bark soil conditioner, perlite, peat moss, and compost. (I put a thin layer of course gravel at the bottom of the pot first - bad idea?). I added some osmocote slow release fert (in pink bottle) and watered it until it flowed through the pot out the bottom. I then left the pot raised on feet with no tray so air could circulate underneath and extra water could seep out. I've been testing the soil with a moisture meter and have only watered twice since repotting it. I've also fed it some fish emulsion. It had some slight yellowing when I bought it, but I'm sure the yellowing has increased.
Thanks for the recommendation of contacting the ag agent.

Okay, you may find that your potting medium is a bit too heavy. For me, in S.California, where I have my citrus outside all year round, and where it is warm to very warm and dry for about 8 to 10 months out of the year, I can get away with 3 parts cactus mix, 1 part small bark chips and 1 part perlite. I never bring my citrus inside. You being in zone 7 means you'll have to bring your citrus inside for some of the winter, I'm guessing. And, yes, gravel at the bottom doesn't do a thing, so pretty much a waste of time. I would be more inclined to use the 511 mix as most container citrus folks do on this forum, especially those with wet summers, and in zone 7 and under. Sounds to me like you were at the beginning or some root rot, so it may account for the irregular chlorosis. Lemons need more N in ratio than other citrus, especially Meyer lemons. Probably due to being such prolific fruit producers for sunch an extended period of time. My Meyer lemon has fruit on it nearly year 'round.

If you're using Osmocote, which is an excellent time release fertilizer, you want to use Osmocote Plus. It sounds like that's what you have (Osmocote Plus Indoor/Outdoor fertilizer). We pitched such a fit with the company that they product the stuff back. It is really, really exceptional for potted citrus. Once your tree starts to recover, you can add some Foliage Pro to your fertilizing regime. Very excellent product, great NPK ratio, all the micros as well.

Watch your watering. Your tree has a pretty significant canopy, so if the roots are compromised, don't be surprised if you have some leaf drop. It is going to take a bit to have the root recover, but it will, as long as your potting medium isn't too dense and heavy, and ends up getting all soggy, again. Which is why I think you should consider changing up your potting medium, which was the issue to start with.

Patty S.

Thank you Patty,
It is the osmocote plus I used. I'll get some foliage pro too.
The potting medium is drying out quite quickly, 2-3 days after a good watering, my moisture meter says it's almost dry 8" deep. It drains well, but maybe too well, if it's not retaining moisture for long?
I'll look at the 511 mix you mention. I read somewhere (after I repotted) that if root rot is suspected, adding a little hydrogen peroxide to the water would kill any bacteria. Would you recommend that? And if so, should I repot and dunk the roots in the hp solution, or water it with the solution now to see if that helps the roots establish, before repotting again?
One more thing, I noticed a white spider that had created a tight web that held two leaves together when I first got it home. I nixed the spider and cleaned off the leaves. Just wondering if that may be relevant.
Thank you so much for your help!

Overall your tree looks pretty good having been recently potted up. I would leave it as is for now, letting it get a chance to establish in its new mix. Al

It's a Meyer, which in containers has a deserved reputation of being finicky.. You have likely changed the light conditions significantly and Meyers do not deal well with that; they may drop many/most/even all of their leaves, to be replaced with new leaves better suited to the new light conditions. ALL citrus suffer from transplant shock; so I would not despair. Your have been given good advice here; take it, do it; and your tree should be fine in the future.