Weaponsmithing Melee/poison Weapon Question

This is the prototype of the weapon
As you can see I want to utilize this weapon with poison, so curse would be welcome, however - should I replace one elephelk trunk with an earth or water powder?​

 

Not certain, how do powders on crafted weapons work.

(I like the idea though)

 

Adding a powder as a crafting ingredient only affects damage, when you craft the weapon it comes with powder slots and you have to add the powders to get Curse yourself. At least I think that's how it works. What are the powders for?

 

Powder would simply be for more damage, 20 dura may not be that much of a difference and I lose 30 sp req too

 

I'd honestly go earth because it does more damage but if you're gonna use this with Necrosis it doesn't matter really