About the copper sulfate...
The bad guy is the copper, like silver, chrome or mercury. This metal in itself is very toxic for most of the organisms.
A small amount impairs the growth of algae, lichens and other fungi in the pools or on the roofs.
Put a coper wire along the top of the roof, and only by the very small amounts taken by the rain drops, your tiles will stay clean, without algae, lichens nor moss.
Avoid the contact with iron or other metals, though.
For the roots, the tree "knows" nothing about the bad neighbor in the drain trench and therefore it can't want to avoid it. But the tiny roots found it on their way and they are killed, or at least they stop their growth. Other roots around don't have this problem, continue their business and take the leadership. So, the drain stays clear. Until the coper concentration comes low enough to allow the root's growth...
The sulfate coper is a very soluble form and doesn't stay long in place. It's curious that it was used to preserve wood.
It's used for treating the vine but it's quickly washout by the rain and it has to be mixed with calcium carbonate to last a little.
