|Your Banded Trochus Snails are spawning. They reproduce sexually by releasing gametes into the water column. The gametes appear as the cloudy white substance you observed. This relatively common occurrence is frequently sparked by changes in lighting or water conditions. After the gametes join, the developing larva is called the pelagic stage, and is free-swimming. Later, it settles into the substrate where it develops into a mature snail. To increase the chances of the juveniles reaching maturity, turn off your protein skimmer for a week or so when the snails are spawning. Within a few months, the miniature Banded Trochus Snails will begin to appear.
A larger population of Banded Trochus Snails is not detrimental to your reef aquarium. In fact, these snails are well suited for reef aquariums. They control algae and diatoms, remain small, and typically do not displace corals or rocks. Plus, because of their shell shape, they are not easily eaten by crabs, and are able to right themselves when necessary.