I had dozens of snails living in my filters that I used to pick out and feed to clown loaches every week. I went to harvest some snails tonight, but found none! I usually see a bunch right away. I was kind of surprised. I recently changed the substrate after moving last week, but can't figure out what would make them disappear. They get lots of food coming to the filters. Would a possible ammonia spike kill all snails but not fish?? Do they hide at night??