dead tree

[thefishguy]

I have this thing in my tank that looks like a dead tree. it is somewhat seethrough with a brown color. it branches out and, it isn't stiff it waives in the water, and when my hand gets close to it is retreats, or shrinks itself, it gets shorter

 

[Fluff]

The only thing I can think of that fits your description (excpet for the shrinking part) is a branching type sponge.

 

[Serge]

Possibly some type of feather duster?

8)

 

[Florida8]

Apistasia maybe???