Meyers do not handle changes in light, temp, humidity well; they do a little better, if you can make the adjustment gradually; i.e. sun to partial sun, to shade, then indoors. In Zone 4 I would probably opt for leaving them outside, covering with a blanket or light tarp with a 75 watt bulb inside on cold nights; and only bringing them inside on the coldest nights, then back to the sun as soon as the temperature gets above 30 degrees F. The tree will do better outside always, as long as the temp. is 30 or higher. When you make rapid light changes, the tree drops the leaves it had grown for sunlight and tries to replace them with more efficient leaves for low light. I understand that I am anthropomorphizing here, but I hope you get the idea. For the rest of this Winter, I would leave it where it is and in the mix you have; it might not survive another shock at such a young age; as the tree grows it will store more carbohydrates in the trunk and branches that allow it to "suffer" more without major damage. When you can put it out in the Spring, that would be the time to make another change in the mix. BTW, if you posted this on the Citrus forum, there are lots of folks there that could help you better than I.

Temperature is prolly not your issue given your zone and plus it's a Meyer--they fruit here in winter really well. You may want to make sure that it is getting enough water to help with fruit set, especially at this warm time of year. Of course you don't want to overdo it, but it can be a fine line to walk. Sounds like it is getting the proper nutrition with new green leaves so I don't think that is the issue. HTH.

Looks just like a vigorous growth to me; happens a lot with my garden trees and also my field trees. The difference is my field trees get pruned back according to our defined spacing; while in my garden trees, I tend to let those go for awhile; if it has no thorns, it is not a watersprout; and if the leaves look the same it is unlikely a sucker. If you like uniformity, you could lop it back, which will encourage branching and also more growth in other parts of the tree. In my experience that branch will likely bloom and produce fruits in the Spring; and the fruits will weigh the branch down and create upward growing shoots from the "sides" of the big shoot.

I just started fertilising 2 weeks ago. I used the seaweed liquid fertiliser 'seasol' and i just added some dymanic lifter pellets. I did some reading and i added iron chelate and iron organic fertiliser afew days ago.