Cody one of the main reasons I like a mixture is because yes snails are good for some clean up duties, but not all, and the same is said for the crabs. If you got a mixture, they would will have a larger variety of nuisance algae or organic material that wont be causing bad water quality. Plus crabs are fun to watch
Sorry ThalesthePearsei, but I've never really looked deep into snail species...
When I have bought snails in the past I first bought them off of Dr. Mac's from Pacific East Aquaculture in a package (I got some great corals for a good price with them too
) for my 560g display tank.
Then for my smaller nano reef tank, i got some from my LFS and they were sold as miscellaneous reef clean up snails, so i dont really know what I have roaming around in there
One question I've always wondered but never asked is if we could, or should put snails in a refugium.