Is this sponge

[Alexmcm81]

Can someone tell me what this is? Is it sponge. Just came back from a 3 week holiday and before I left I had a few of these white spots. These are now all over my sump and the stuff on my gsp frag is everywhere. Any advice is appreciated

 

[ISpeakForTheSeas]

The white spots are Spirorbid worms - harmless filter feeders.

These are sponges, yes - harmless filter feeders.

These may be sponges too, but if they're growing over the top of a coral, they're definitely not harmless - given where it's growing, you may want to just take coral out and dip it or something and try to remove any leftover sponge you find in the tank too.