What is this??

[Chrysus]

I wasn’t sure what section to post this in because I genuinely have no idea what I’m looking at lol.

These weird things have been growing on this heater for quite some time. We have another identical heater on the other side and it only has the small dots on it. What are they?

 

[Crabs McJones]

Looks like Pineapple Sponges and Spirorbid worms. Harmless filter feeders commonly found in sumps :)