The Nerite and Turbos will eat algae, the Nassarius are carnivorous and will eat uneaten food in the substrate as well as voraciously go after whatever food you put in the tank.
To make sure they don't starve, I target feed mine (4 of them) about every two weeks with a small piece of fish. I wait until they come out very active at feeding, they don't always come out every feeding. Then I take a small piece of fish/scallop/mussel and hold it next to them with tweezers until they grab it.
It is astonishing how much one of those guys can consume.
They are also good to have because they stir up the substrate.
I also use Hikari sinking algae wafers to help supplement the algae eaters in the tank. All the crabs love them.