This is from
http://www.aquariumpros.com/faqpro/pests_1.shtml
I have noticed a build-up of what looks like tiny pieces of salt along the walls of my aquarium. On closer inspection the pieces are actually small spirals that appear to be hollow with tiny bristles near the open ends. What are these?
Those are baby hard tube-worm feather dusters. They are naturally occurring, harmless filter feeders that eventually show up in almost all reef tanks. You can scrape them off the front and sides of the tank with an algae scraper, but let them grow in the back. They get larger and beautiful when they get older, and help filter the water. They have beautiful calcium-based shells which form complex spirals and curves, and appreciate a calcium level of about 400ppm, with some strontium and magnesium added periodically. Some hard tube-worms can live for hundreds of years. The only problem they cause is that they also will grow inside pumps, where their shells can damage impellors, so pumps should be cleaned periodically to remove them, but you should be doing that anyway.
