每日吃瓜

I am new to bonsai and am struggling to keep my one plant alive. About a week before Christmas my uncle, who is a bonsai enthusiast, bought me an "arboricola" bonsai as a gift. The plant came from a bonsai specialty nursery so I assume it was well cared for before I got it. It looked healthy when I got it but did have some sort of white film on the leaves like it had been sprayed with some type of treatment, not sure if that has anything to do with its problems. After a couple of weeks it started dropping leaves here and there. Eventually the rate of leaf drop accelerated significantly. Some dropped leaves were green but many were a blackish brown. I did not over water it but may have under watered it. Eventually all leaves had fallen off but the branches were still green and appeared to have leaf buds on a few spots. So I kept caring for it. I removed it from it's substrate to check the roots for bugs (I figured it was a goner so wasn't too concerned with disturbing it). I tried a few things to increase humidity around the plant because the branches were creased like it was not getting enough water, but eventually struggled with fungus and just stuck it back in the pot with pumice as substrate and watered it once to twice a week. It did nothing for two months.

Then all of a sudden in April it started to grow in one spot. It grew for a little while and then turned black and died. Another shoot came out of the same area, and some growth started in another area too. These clearly started to turn into little leaves, then turned black and died. I have sprayed it with insecticidal soap twice since the growth started in April just in case that was the issue but it hasn't helped. There are many spots of new growth and I'm just afraid they're all going to die, I need to do something. Does anyone know what could be causing this? I know having it in straight pumice isn't ideal but I've just been worried about upsetting it now that it has actually started to grow.

Here are some photos of it's current condition:
Original growth that died:

Second area of growth that died (plus some potential buds):


Current living growth:

Do you know what species of tree you have?
Also, where are you keeping it? I hope it is not on that table permanently?

It is a Schefflera arboricola. It has been indoors since I got it, first because it was winter, and now because I'm overly concerned about shocking it and killing off the new growth while there is so little of it. To introduce it outside would I harden it off like I do with veggie seedlings? Do you think I should start doing that now?