Cholla wood is the skeleton of a cholla plant. It’s full of holes, but hollow inside. I used it exclusively to hatch out baby plecos, because the wood gets coated with biofilm and the fry will feed on these exclusively for the first 3 – 4 days when food is critical. Also used by shrimp keepers for the same reason. They usually sell for $4 per 4” piece. There’s 15+ pieces here.