hey guys,
so my brother has a fire thorn bonsai that we bought from a bonsai shop a few months ago since then it has gone from nice and green to losing its leaves twice both time before winter, and now it doesn't look too good. The dirt is hard and isn't very loose at all so I think the reason why the bark on the tree is literally withering is because it isn't getting the water that and nutrients that it needs. I was wondering what kind of soil that this tree would like, and when is the best time to change the soil. Thanks in advance

sorry forgot to add that I have been keeping this tree inside along with my other trees because it is very cold where I live, in the winter time. I live in Michigan on the East side of the state. My house stays around 60(F)and I have it by a window so that it gets sunlight, and have been watering it when it is dry but the dirt is so hard that I can't really tell when it is dry or not even when I touch it.

Did the vendor tell you it is hardy and must be outside? Well it must. Sounds like it has also been dry, but the leaf loss if it was outside would of course be normal.
the temperature is far too high for this species. You may well not get it back. If it must be re potted then it is done in spring.

yeah, they told us it was an out door tree but my brother kept it in the house during the winter and he didn't water it at all I was the one that was mostly taking care of it... I couldn't save it and it ended up dying about a week after I posted this.. So I cleaned up the pot and put some new and better wire in it and now it is waiting for a new tree, I'll probably end up growing one and putting it in that pot.