Turbos and live rock

[Salty Cracker]

Can some explain to me why my turbo snails will only go onto one half of my live rock, and not the other? I ordered 20 pounds of live rock and it came in as just two huge chunks. The turbos I bought will only stay on one of the rocks. The other chunk of rock is covered in brown crap from the die off. All ten turbos stick to the same rock that's nice and clean. Could it be the shape of the rock? Even when I place them by hand, they make their way to the clean rock.

 

[Xavibear]

There is nothing on the other rock that they want to eat. What is the brown crap? If it's cyano, they won't eat it.

 

[E46Twist]

The same reason they always run for my algae clip