What have you been doing?
I removed snails by putting out veggies at night and pulling them up in the morning with all the snails. I also squish any bladder snails I see on the glass. Cruel but effective.
Thanks Simon. I hadn’t thought about the heater, that could be a possibility. As could breeding damage, as I have males and caves, though I haven’t seen any breeding behaviour. It does look like marks and not protruding. I’m thinking it’s probably a heater burn, and I think they will go away on their own, yes?