I don't think a longnose will eat shrimp - maybe tiny ones. I would get the snails and get about a dozen peppermint and 3 or 4 skunk cleaners. Make sure your sand bed is WELL populated with worms. The worms will quickly dispose of uneaten food and detritus. The shrimp will also clean up and eliminate the source of nitrate. You can get a few shrimp at first and see if they are safe. Pepps are cheap enuf to experiment with.