What is this?

[ASIN28]

What are these I started noticing them on my back wall in the corner and on the mag float? They don’t move or anything. Thanks

 

[eggplantparrot]

spirorbid worms.

harmless filter feeders but can get out of control if you feed way too much.

simple acid bath will get rid if them

 

[Gernader]

+1 to spirorbid worms

 

[Soren]

Also, you might want to be careful with both leaving your cleaning magnet in the tank and having spirorbid worms, since the worms may create calcareous tubes on the scraper surface that will then scratch your tank sides.
My 75-gallon FOWLR has many scratches in the glass, and I suspect this is the reason: the previous owner did not notice that leaving the cleaner in the tank resulted in trapped calcium carbonate bits to scratch the glass even if being careful not to pick up sand while cleaning the surfaces.