I bought it at a bonsai store in a Long Island, NY mall last year around this same time, perhaps a month or so earlier. It was labeled: "Banyon tree, 15 years old, 6 years in training". I bought it for my mother in law, who was going through chemotherapy - she joked with me that it was my responsibility to take care of it. Well, when she passed a month later, her husband gave me the tree. My point, I guess, is that I'm rather emotionally attached to this tree, so I am desperate to figure out where I went wrong and how to salvage this little guy.
The tree is about 10 inches tall from the base to the top. It's in a rectangular dish about 8 inches in length. The trunk is about 1.5" in diameter. The soil smells healthy (is that even a thing??), but is covered by a thin layer of moss. There are very few little pebbles on one short side of the dish. And when I touch the soil/moss area, I feel a bunch of wires or staple type things.
I've kept it indoors.
I've regularly submerged it in the kitchen sink with some blue fertilizer powder the store gave me and let it drain before putting it back on its little tray.
I've changed it's location from time to time (which I now understand can shock the leaves to fall) - trying to keep it away from cats who aren't kind to plants, and trying to give it a place where I could still enjoy it but it could also get some window light.
There is one main trunk and primary branch that has nothing on its 3 thick stubby branches. On a secondary offshoot there are about 4 long thin empty branches. And then there's a single new growth shoot coming up off the trunk from a lower area. (I haven't known what is god to trim or keep, so have prob done it a bit of a disservice by letting it mostly do its own thing.)
There's a bit of a dark green coating on the trunk about 2 inches up from the base that takes up about an inch of space. (Is that a fungus or is it normal/ok?)
As of right now, there are ZERO leaves. And the new growth areas have turned dark and shriveled up.
It seemed to do the best a few months ago when it was in our tiny south-facing master bathroom (which we don't use to shower, but has a window), sitting on top of the toilet bowl tank (it was the only large enough surface). It had great waxy looking beautiful green leaves then. I moved it to my bedside table eventually where it would have more space and where I would get to see it more often.
Unfortunately, I didn't realize that drafts were bad for ficus trees. Apparently they're super sensitive to changes, from what I'm reading. I had our whole house attic exhaust fan on for a couple hours in the mornings and the ficus sat in front of a cracked window shaking from the intake of air. I think that started this downward slide, because that's when it started dropping leaves frequently.

I moved it 2 weeks ago and started seeing a couple little leaf shoots start, while some of the larger leaves still continued to fall occasionally.
And then a few days ago, the 4 clusters of leaves that this poor tree had, ALL suddenly pointed downwards. 2 days later, they were all curled and dropped. And the 2 little new leaf shoots that were barely a 1/4" in size turned brown and withered in place. Even the new 3" green trunk offshoot of a new branch is now brown and shriveled.
My bonsai is now a brown husk!
I have no idea what to do. I am desperate to help this little tree, but don't know if I should be buying something to feed it or apply, or placing it outside where it can get more sunlight, or letting it dry out, or cutting back these dead looking branches so it can focus its efforts on the main trunk right now...?!?!?! I have no clue.
Please help. I don't know how to go about trying to give this little guy a fighting chance to bounce back, but desperately want to try. I just need some direction.