maple bonsai blackened disease

I thought the sickly leaves could be handled by better soil and fertilizer, but then I took a closer look at the bark. Ive been aware of something going on there for a while but thought it might be a weird thing arakawa does when forming rough bark. The discolored area is spreading and now...

Hi guys, Hope you all well. I have given 30 years old maple bonsai tree, 3 weeks ago. And already have blackened trunks but not as bad as this. 3 weeks ago still have new small trunks and small leaves to start growing. Last week i have repotting the tree, cutting a lot of roots, with hope i...