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Saltwater Aquarium/sponge/worm/?? coming out of rock and upsetting Acan


What is this and is it harmful to the tank? There are several of them (mainly coming out of the same rock) and the Acans that are on the same rock are not getting along well with them. They are attached somewhere inside the rock. Please help! And how can I safely remove them without possibly harming anything else in the tank?

Hi Tracy:

It looks like a species of sponge, which are harmless. It should not cause any harm to your Acan Coral.  

I wish you the best of luck with all of your future saltwater aquarium endeavors.


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David Ocreef


Technical saltwater coral reef related aquarium questions are welcome. Coral, invertebrate, and peaceful species of saltwater fish questions are welcome. Questions asked on Saturday and Sunday will be answered the following Monday. REMINDER: Please check the answers pool to see if your question has already been asked and answered. Questions typically are answered within a 48 hour period, however sometimes it may take longer.


I possess over twenty-five years of hands-on experience and knowledge in the ecology of aquariums. Beyond the traditional, I have successfully tested and sustained environments that have been uncharted territories for hobbyists, for decades. I am the first to admit I don't know it all because there will always be something new, amazing, and exciting to learn about, as discoveries are made. It's a hobby one can never outgrow, or grow tired of.

MASNA - Marine Aquarium Society of North America. Director of Orange County Reef Aquatics -

Publications,, and many others.

After High School, my experience and love of marine animals influenced me to take up studies in Marine Biology. Throughout college, I studied Microbiology with an emphasis on Marine Life, as well as numerous other sciences. I continued to advance in this hobby, by building a dozen or more saltwater ecosystems all utilizing Microbes as the major source of my filtration method.

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