My Pachira Aquatica is losing its leaves. Help!

[o2tha1]

Hi everyone

I'm new to the forum, this being my first post, so I hope there'll be no issues with my post.

Moving on though, for the past couple of months the leaves of my Pachira Aquatica have been browning around the tips and some around the edges. It was pretty contained at first, which is why I didn't worry much, but now several leaves have yellowed and the browning is spreading. I even picked off an entire branch which had dried up.

I've had it for about a year and half now. For the first year, it was in a very sunny room, however since I've moved, the window to the room is very small and I believe especially now, in winter, it's not getting much light, but there's not a lot I can do about that. It's also placed near a radiator, but this has been the case for the past half a year.

Another issue which may be completely unrelated (but might not me) is that it's got a small wet patch on the base of the trunk. I've reduced the amount of water I give it every time (to about half) since I first noticed the problem about four months ago. It looks like it's improved a bit but not much to be honest.

I've attached some pictures I have from different stages which I hope will help.

Thanks for any advice you can give me!