Dark pool, holy pool, sword pressure, ect.

[Viladin]

These abilities all allow you to enhance, temporarily, your weapon. But what if you weapon already has the maximum enchantments it can have i.e. +5 longsword with +5 abilities. Does this pool become worthless or can you place up to an additional +5 abilities worth of enhancement on it via the ability?

Yes, it becomes worthless. To a degree, most pools have alternate abilities that can be activated.