We use turbos and hermits as well, although in our O. scyllarus tanks, there isn't a snail large enough that a 15 cm animal can't crack. We try to control growth in those tanks by keeping the phosphate down, removing large growths of algae, and by keeping lighting to a minimum.
I firmly believe that lots of algae, particularly greens and corallines, are good for stomatopods. I usually only worry when we have an outbreak of red slime and green filamentous algae. Our animals maintain much better color in tanks full of algae, they reproduce more frequently, and they live longer.
Roy