fewer gastropods

I didn't have an overpopulation problem again yet, but someone on the planted tank forum asked so I picked out about two dozen malaysian trumpet snails to sell and mailed them this morning. Why is it that when I don't care about finding snails, they're all over the walls of the tank at night, but when I want some, they are hiding and I have to search.

One of my red tomato nerite snails died. For a few days it looked like was nearing the end- I found it several times lying upside down or on its side. Turned it upright and it would move a bit, but then fall over again. I pulled it out of the tank yesterday- it didn't smell bad yet but the operculum was loose so it was over. I am not surprised or sad, really- at best guess I'd had this snail nearly three years.

I think I only have two nerites in the main tank now? one tomato and one zebra...