Hmmmmm... i'm not 100% sure... but why not try breeding Ramshorn snails? they are freshwater and only require a 5-10 Gallon to start breeding like wild-fire, or if you can get them, Marble Cray Fish also reproduce reasonably quickly if you can get a 10G+ for them...
With that being said, if your only after crunchy foods, you could always feed your fahaka Mussel on the shell to help keep their beaks worn down...