Is this a pest?

[itafx]

Lots of these appeared mysteriously in my SW tanks. They look like elongated whitish tubes that anchor on things. At the same time these appeared, my macroalgae started shrinking instead of growing. Are they sponges? Are they harmful?

 

[Innovator]

They look to be q-tip sponges, of the calcareous Syconoid.

 

[Kurt_Nelson]

Yup... sponges. Harmless. They'll come and go as the nutrients come and go.

And you ARE scrubbing out that sponge filter on that BioWheel (100?) every week... right?

 

[itafx]

I'm using an Emperor 280. I looked inside and saw these sponges all over the insides of the filter media cage. I scrubbed them out and totally cleaned the filter. I cleaned the sides of the glass and am about to do a 50% WC. Glad the sponges are harmless. Thanks for the replies.