A couple of apple snail questions?

theres only two questions, first of all and most importantly, my previous apple snail came to quite a nasty end when it 'slithered' over the filter and got sucked into it :( i've lowered the filters suction to the lowest it will go but will that be enough to make it safe for the new snails, or is there something else i can do. Also, my previous snail lived off algae and fish food that sank to the bottom but i've been told that i should have fed it vegetables like lettuce and cucumber ect, is that true? thanks