Algae eating snails that DON'T reproduce?

[Erik the Furry]

I think nerite snails only reproduce in brackish water so that might work for you

Correct, they need brackish water to breed - which somehow implies that the ones we get in our shops could be wild caught.

Mine were also not very prolific algae eaters. Think they need to be hungry before they eat algae and with messy eaters, I would not be surprised if they opted for your oscars' leftovers instead of algae...

 

[AaronKWolfe]

Is the Oscar likely to try an eat them - and choke to death on the shell?

No, the Oscar may eat the snails and crush the shells. Mine loved snails!

 

[phreeflow]

Agreed...Oscars will eat the snails

 

[The Silvs]

Maybe something like an ottocinculus may do the job Youre after. They may also become scram for the Oscar though. You may get away with it. Only a tiny fish, he may not be too fussy after the first day or so. Risky!