The notocyphus IME doesn't make a wonderful carpet. I'd go with a MP or xmas carpet and fissidens accents if I were you. Try dry starting the MP on cinder gravel. I'd go with a loofa or hairnet on cinders for the mosses. Those stones look like A LOT like coral. I'd be wary of using those with shrimp. I personally would replace them, but if you are sure that they are inert (test test test!), arrange them so they don't point in all one direction.