Anybody know what this is

[nyshoots]

I was doing dome cleaning and I found this big white mass on the underside of a rock. It looks and feels kinda like silicone but its not and it wasn't there a month ago

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[Josh]

Probably a sponge.

 

[TRIGGERMAN]

yup sponge

 

[Reef Reaper]

Definitely a sponge. Not harmful.

 

[jr973]

Definetly a sponge nothing to be alarmed about that's beneficial to your system