Someone correct here if I'm wrong, but I believe...
You're mistaken. Nassarius snails are scavengers, not algae eaters. They are beneficial to a DSB because the help turn the sand very slowly. They are beneficial to a tank because they eat left over food and decaying stuff that settles on the sand. Mine tend to hang out under the sand until they smell food, then the go nuts. Some go up the glass lookign for food, some travel along the sand. I don't ever recall seeing them on LR.