I got some like that out collecting one day.
they sink relatively fast, I just boiled and baked mine and put em in within 5 days they were down.
I am going back to get more but I do have a shrub stump in the shed I yanked out with the ATV a few months back. I am lopping the roots off at the trunk and got approx 200 "branches" to attach the moss to, only problem is it doesnt fit in my tank.
What kind of wood is that?