tank health

I recently bought a new fish tank and there are these weird white balls forming in the corners of the tank. Is this cause for alarm?

Hey all, Found 10+ little worms cruising on top of the sand substrate in my 55 gal. They are black, kind of segmented, and just under 1cm long. This tank has regular 30% water changes, weekly. There haven't been any issues, as far as tank health, since the tank was setup over 6 months ago...