now i was told that they will only grow to fit in the shell so if you hve no extra ones they will only grow in to the shell they have now. i have had all of mine for about 6 months and i have 2 diferent types and i have only lost like 2-3 of them. if that. i never did a real count of them when i put them in but that is just a guess from what they said the shipped me. but i can get a good cound every once a wile. so i dont think you really need the extra ones.
A 46 gal
bow front (Soft coral) reef tank with a 10 gal
sump. And a 30 gal
and Clam) reef tank hooked up to the sump of the 46 so they share water.