I have an invader

[u/Jo_51]

I happened to be layed watching my big 120litre tank an I spotted a bladder snail, not got anything new in months, which makes me wonder do I have more of these dudes hiding that I haven’t seen? I read somewhere that they are great for cleaning tanks, an my readings the last couple of weeks I’ve not even had to change water just top it up. Could these be linked?