[I would get some scarlet hermit crabs, these hermits are agressive than others. IMO And yes some nassarius and maybe a conch or two depending on the size of your tank.]
[Nassarious are scavengers. They come out when there is food in the tank. They are awesome for keeping the top layer of your sand turned. Im not so sure what eats diatoms, but if your setup is relatively new they should go away on their own.]
[Fighting Conches are great for getting rid of diatom/algae growth on the sand bed. You usually want to give them a 2'x2' area of sand bed space (doesn't include LR) per conch.
]