Problems with salix tree. bought a small salix tree 7 years ago.?

we bought a small salix tree 7 years ago. pink tips on the leaves and the branchesthin and hanging down. now, for some reason, all the branches have algae on them, they are thicker, but the branches don't hang down. wondered whats happened and if anything i can do. haven't pruned it at all. does it need feed and if so what.