I have some extra Akysis catfish on hand. They don't grow more than 2.5". I was thinking of breeding them, but from what I've read it doesn't seem likely. They aren't strictly nocturnal or even particularly shy. At any given time I see at least a few lounging around in the open. Typical catfish when it come to feeding, they eat anything until their bellies are round. Not a threat to neons, but will eat new livebearer fry.
For reference, the ramshorn is about the size of a small pea.
Just unbagged, in a 5 gallon bucket: