I'm using the standard 5 mm Floridian crush coral to hold onto my floating ricordia, however hair algae sweeps in from the main tank and is colonizing the gravel. My tang doesn't seem to be able to clean it like he does the glass and other fixed objects, I'm assuming that's because the gravel comes up, when he tries to bite off the algae, or he doesn't go for the tough hair algae balls that settle on the gravel as opposed to fresh shoots. I'm definitely looking for herbivores, not sure if sand shifting snails are effective for this situation. I believe hermit crabs would work, but they are so short lived, so I'm looking for a snail with a longer lifespan.