I agree w/ Steve, astreas aren't very hardy in warm reef tanks IME
. Some of the first snails I bought were B. trochus and I still have most of them. Also, I see you have 2 yellow watchman gobies. If you have a pistol shrimp w/ them it will quickly discover that the nassarius snails make good doors/barricades for it's burrow. I can't keep nassarius b/c of this. Good luck.