Another question. Are either of your fish acting strange? In particular, are they rubbing against anything in the tank. What you're seeing could be the dead adult version of an anchor worm (technically a crustacean).
I'm not saying that this is a likely suspect. Instead, by searching "white worm aquarium", this was about all I came up with. It could easily be something else entirely.
I would suggest making a worm trap as listed on this page
http://www.algone.com/worms.php
and see if you can get any culprits. As I said, what you're seeing might be an adult or a deceased specimen. What you get with a trap will likely be alive, and perhaps more easily identifiable. You might not get anything, but if you do, you'll at least be able to identify it and figure out if anything needs to be done.