Tank covered in what look to be chitons at night.

[Queeery]

This is a recent development, over the past couple of days or so. At night, my rockworck is covered in small creatures that look like chitons. I haven't seen a single one move. A couple of them are shaped almost like pyramids. Are these harmful if there are too many of them? I only see them at night with a couple of exceptions.

 

[Soren]

This is a recent development, over the past couple of days or so. At night, my rockworck is covered in small creatures that look like chitons. I haven't seen a single one move. A couple of them are shaped almost like pyramids. Are these harmful if there are too many of them? I only see them at night with a couple of exceptions.

It's hard to see in your picture, but they may be limpets. They are conical in shape, are more active at night, and reproduce fairly readily in aquariums. They are typically considered beneficial clean-up crew, but can sometimes reproduce at annoying rates.

 

[ISpeakForTheSeas]

They sound more like limpets than chitons, but the pic isn’t really clear enough to tell for sure. Either way, chitons and limpets are both beneficial and shouldn’t cause any problems- they should just eat your algae.