What is on my back wall?

[Osc556]

Went away for the weekend and came home to this on the back wall. It is about 8” tall and extends 12” wide near the sand bed. Wasn’t there on Friday afternoon when I left . Anyone know what it is?

 

[Miami Reef]

Is this it? https://www.reef2reef.com/threads/worm-tree-root-thing.979581/

Search for @ISpeakForTheSeas ‘s post

 

[Osc556]

No it is white and flat against the back wall. It doesn't move or make contact with the sand bed at all. It’s about to spend some time this my glass cleaning magnet