As Sam already mentioned, I too have not seen any negitive impact on the reef. I have 4 of both variety's and have found that even though they don't eat much due to there size, the benfit I like for using cowries is they can get into small places where my hand, cleaning magnet, or snail's just can't fit! I see the cowries a lot cleaning in tight spot's between the rock and the glass and in other small area's too like behind my MJ1200 and around the ellbows on my returns
IMO-there worthy little house cleaners
