What is this stuff

[finley]

This may be Norma not sure ! I am cleaning my filter sponges and have seen this on them, is this normal ? I assumed things like this would be caught by the filter sock

 

[Dan_P]

Between the filter sock and pump inlet, things grow and die. Totally normal. If you have a microscope, you could possibly tell what organism produced this. It might also be calcium carbonate.