Turbos and Astrea are poor choices in a Nano because of the size they will obtain; I'd recommend cerith and nerites as they will do an equally good job of munching algae while not growing too large for your tank.
If you have an LFS in the area willing to trade out livestock as it grows, then the turbos are okay.
Again if willing, a Queen Conch is an excellent scavenger for keeping the substrate clean and eating the tougher forms of micro and macro algae.
Most LFS would prefer to have larger conchs for their customers, however within the trade most arrive at merely an inch or smaller.
This is a perfect pairing for Nano keepers and their LFS if willing to swap.
Ed