I suspect your soil mix is WAY TOO HEAVY!!! In general, I would NEVER recommend anyone to buy a prepackaged citrus soil mix!!!! Now maybe because the nursery carries it may be okay but I am still skeptical,especially when you said you only water once a week. If it is growing in a healthy mix for the tree, which means a porous mix that rapidly drains the water after you have watered it, should need watering 2-3 times a week.

Could you post a picture of you tree's soil? I have a feeling this is you major issue. 4-5 years ago, I bought a moro blood orange, and I believe a meyer lemon or a tangerine. Anyhow, I bought Miracle Grow cacti and citrs mix. I potted them up, and put them under my grow light. Within a week, they completely defoliated. Within two weeks, tangerine was dead, and blood orange was barely hanging on. When I knocked them out of there pots, I could smell the dank, rotting roots. Citrus are OVERLY sensitive to wet feet. In the citrus belt, the combo of sun and heat helps to dry out there soils but for people that don't live in sub tropical/tropical regions, it is imperative to have soil that drains efficiently.

I don't want to go into all the specifics on making mixes but if you search on this site for Al's gritty mix or Al's 5.1.1 mix, it will show you how to make it and also explain why it works so well. Some people, myself included, have had difficulty finding all the components to make it, and I had to substitute certain components for other things. The bottom line is this. Whatever you end up with, when you water, you want to see water flowing out of the drainage hole within seconds of watering! Also, make sure you have a pot with adequate drainage holes(One large hole in the center is okay but personally I prefer several holes. When you have your tree indoors, if you have to we a coaster to collect the draining water, empty it right away. You do not want that water sitting there!

It took me a year or two to be able to understand what makes citrus trees tick. I won't tell you that I am an expert because I am sure there are still things I could be doing better, and I also know that I will always learn more from reading books, and from learning from everyone here, but in my opinion, it's all part of the fun!

I am sorry I couldn't fully diagnose your problem here but I feel confident that once Meyer Mike, Patty, John or any of the others read your post, they will be able to help you out.

One last thing. I was curious about the height of your tree, and did you think the growers price was fair? Not that I am on the market for ordering anymore citrus. I have enough right now.....well?!?!?!

Andrew

Your plant is suffering from transplant shock and from significant change in light conditions.
When you dramatically change the light conditions a Meyer will drop most, if not all its leaves, to replace them later with leaves better suited to the new light conditions. To move a Meyer from outside to inside without the leaf loss, you need to move it from full sun to partial sun for 2 weeks; then to full shade for 2 weeks; then indoors; reverse the process when putting it out in the Spring... and please DO put it out, if you can; you will be rewarded with a happy, healthy plant.
Second, when you bring it indoors to a sunny window, the plant gets warm; but the roots generally stay cool; and citrus roots don't like to grow into cool soil... the solution is to put some sort of heater to warm the soil, or to put the plant a little further from the window. The thing to remember is first the roots grow; and then the leaves and branches.