I bought some astrea snails last week, now these go to town on hair algae. even the tall stuff. after acclimation I placed them on the "problem" rock that I have. they stayed in the same spot nearly all night, just munching a thick spot of hair algae. it's kinda funny though. I allready had one astrea, and he is the laziest snail on the planet. he will sit in one spot for days and never move. I have actually poked him with a stick a few times to make sure he was still alive.