As far as I understand from reading the wiki, it creates a GUI element. This means that you are to treat it as any other GUI element, not like dx functions.
Basically, there's no need to render it yourself using onClientRender -> the resource does that for you.
So, what your code does is that it's creating a new GUI element on every render, that's why you're not able to destroy it. You're only storing the latest instance of that GUI element inside of the blur variable.