how big are your clowns?
Mine are currently 5" to 6" long. The largest ones are the MTS hunters. I've
seen them dig huge holes in the gravel looking for them, then pulling them out
and worrying them like a dog with a bone. It can keep them busy for hours.
It takes them longer to kill MTS than pond snails or ramshorns, but they do get
them eventually.
Leigh
http://www.fortunecity.com/lavender/halloween/881/