It is classic Meyer leaf drop from changing light condition. I understand you were careful; had you not been, it would have lost all its leaves. Keep doing what you are doing and you should soon see new growth.

10% bleach solution?? I've never heard of that before!

I was poking around on these forums and saw an older post referencing using a 1 part bleach to 9 parts water solution for treating root rot...I hadn't heard of it either! It sounds a little risky, so I thought I'd see what sort of advice comes in before trying it.

What's the pH of your tap water or fertilizer solution?

Have you 'ever' seen your tree go limp before watering it? Just once in the past year? Can you remember?

It's very easy to let a watering slip by when the mix is fresh or when the roots have not filled the container and not catch your tree limp in the gritty mix. You have to be very diligent about watering)

If you let that tree go into a state of limp, just once or twice. you are talking about root damage and that can explain the root rot.

That is the reason why I switched some of mine out of the gritty mix into the easier 5.1.1 mix or used a gritty mix with a bit more water retentive materials.. I was not diligent about watering and would wait until it was too late to water by accident. I hated that.

Yes, I have seen the leaves droop slightly over the winter months - I have an alarm set on my phone to remind me to water, but if the house was a little extra dry, I may have ended up watering late. The question I have is: having un-potted the tree to look at the roots, should I risk un-potting it again to trim the roots? Or is there a less stressful way to address the situation?

I would give it time to heal. Those roots can easily damage and then rot away when one forgets to water because they have been killed off and take up no water at all. Those brown dead looking roots are from past damage, not from the mix itself.

I would not touch the roots at all. just put some kind of bark or mulch on the top of your pot so that the top does not dry out before the middle and bottom does, keeping in moisture a bit longer and watch your watering.

Wait until you see some active green growth coming on before you fertilize your tree and keep it in a warm bright area, not direct sun.

This is what I would do. These trees are unpredictable and no ones how it will respond to a root cutting or re pot. It all depends on how much damage your roots have and how you are caring for it.

I hope this helps)

Yes,never fertilise a sick plant

Thanks so much, everyone! I spent a long time researching on this forum before taking the plunge on buying a tree to avoid making silly mistakes, but I'm sure I still have a lot to learn. Your generosity in sharing your knowledge is very much appreciated!

Alyssa, mine did that as well when I moved them outdoors. They drop those old leaves and grow pretty new ones. Give it time and I'm sure it will bounce back. I have trees in the gritty mix, but more in the 5-1-1 mix, which I prefer.