Can anyone help with ID?

[Ziggo420]

I have this crud growing on my glass rocks and substrate. I was wondering if anyone could tell me what it is and if I should be worried. The aquarium has only been up since January and I haven't even turned the lights on yet except to watch the fish feed. Any help would be greatly appreciated. Thank you.

 

[ISpeakForTheSeas]

I have this crud growing on my glass rocks and substrate. I was wondering if anyone could tell me what it is and if I should be worried. The aquarium has only been up since January and I haven't even turned the lights on yet except to watch the fish feed. Any help would be greatly appreciated. Thank you.

Looks like sponges to me - generally speaking, sponges are harmless filter feeders (with a few, rare exceptions).

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