Why is my rock got furry things on it

[AgentAlice]

Why does my rock got furry things all over them. Even the Tonga branches but yet I see no diatoms besides what i see on that rock. I still trying to figure out what it is.....but my ammonia and nitrate is 0ppm and my nitrate is 20ppm. But I think it's a false read cus I'm using the strips. I've order a saltwater test with the tubes but somehow I ordered the wrong one. And I see more of these on my rocks too...

 

[KJ]

Sponge harmless filter feder

 

[pletlibo]

Sponge harmless filter feder

Yup. Looks like sponges to me. Don't worry about them, harmless, interesting, and add to the biodiversity of your tank.

 

[saltyfilmfolks]

Some sponges like the same thing diatoms do. Silicates.

So you may have these bloom and and fade just like diatoms.

 

[AgentAlice]

Some sponges like the same thing diatoms do. Silicates.

So you may have these bloom and and fade just like diatoms.

I see them popping up in different areas of the rock. On one of them two sponge thingys is black