Can you identify this?

[ghuffer]

I was adding rock to my tank this evening and found this little white growths on existing rock. It looks like little mold balls or small onion bulbs. I have no clue what they are here are the picture I got of them.

 

[ghuffer]

one more

 

[KevLake2005]

Pineapple sponges. They are beneficial filter feeders
I think they grow fast if there are a lot of silicates present (like silica sand or introduced in the water during a water change).

 

[ghuffer]

So they are nothing to worry about

 

[Matt1351]

Aren't they from not using RO/DI water?

 

[gonpostal]

So they are nothing to worry about

Correct, they're nothing to worry about.

Aren't they from not using RO/DI water?

No. I've had them, and I use only RO/DI water.

 

[MeVsTheWorld]

Nothing to worry about, actually beneficial filter feeders.