[karimwassef]

The ends are mixed, some open some closed.. but there is almost no measurable flow except through the action of the organisms that move in and out of the drilled holes.

Truth be told, I had only planned to use the holes as anchors for coral placement using solid airline tubing. But over time, the vast majority just became access pathways for pods in and out of the hollow PVC.

They're completely encrusted with all kinds of growths outside including corraline. Yellow, pink, white and brown sponges in the dark regions. They don't look like the usual ball or tree sponges though. They're encrusting and form webs or filaments mostly.