snails do not like high flow, that was a mistake. also best way is to start them on the sand until they attach or a week or 2 . use a little flat rock so you can easily move it around. Also you freshwater dip clams, clams and invertebrates are very sensitive to salinity, ph, temp change changes, if you didnt match all correctly it this will kill them. i personally wouldnt dip a clam, just add a wrasse to your tank, and they will take care of any pest.
ps i am a big wrasse lover, i have several in every tank and never dipped a clam and never saw a pest, i have 10 clams already. even love the 6-line. have them in my 80 frag tanks with yellow wrasses. although yellows are more prone to jumping then 6-lines are.
you shouldnt take your clam out of water. it might trap air in it and cause it to die. i have taken them out a few times, but safer not too.
if it was a normal cuc snail, it did not kill your clam. i repeat there was no way it killed your snail.
also not once did you state your tanks parameters, how old is your tank and how often you test. i will assume you know a little about the hobby since you been a member for a long time, but clams are different then corals.