need to know

[stingray 125]

Any ideas what this is, it is like a web or slimey web on 2 pc of rock in my tank?

I know someone will know what this is and I need to know if it good or bad or the end of my tank as I know it now.

The only water parameter off is my nitrate at about 20ppm I am working on it.

Thanks

 

[Troylee]

Looks like a sponge.. Shouldn't be a issue unless it grows over a coral and blocks the light..

 

[stingray 125]

thanks I just do not want it to take over my tank!