Snail Deaths

Question
Hi there, I have two tanks, I bought two gold mystery snails about 6 days ago and added one to each tank.  One tank is a 16 gallon Bi-Orb with 2 small Oranda goldfish (I do plan to move the goldfish to a bigger tank soon).  It has been set up for a month now and is still cycling but hopefully is on the tail end of that.  I do regular partial water changes every other day, ph is 7.6, temp is 72-74.  The fish are extremely healthy, happy and active and I've had no problem with them.  The snail was fine and active for 2-3 days and I added an algae wafer everyday for him.  Day four he sat in the same spot for 24 hours, and I became worried.  I picked him up and inspected him but I've never had a snail before so I don't know what I was looking for.  I didn't notice an odor.  The next morning I was happy to see he wasn't still in the same spot but when I looked up he was floating!  I took him out and he smelled bad and the gold on his shell looked like it was turning brown and black.  I figured he was dead and discarded him.

Tank two is a ten gallon all glass that is newly set up about a week and a half.  It has a cremesicle lyretail molly, 2 variatus platies and 2 african dwarf frogs.  The ph is 7.2, temp is 78 and I am religious about partial daily water changes since we are cycling.  The ammonia never gets past 0.25 before I do a water change.  The fish and frogs seem active, healthy and fine.  The gold mystery snail added to this tank has been active for 5 days, eating the algae wafers, hanging on the glass and tank ornaments but then today I noticed he was in the same spot for 24 hours.  He does not have an odor and his shell is not discolored but he is hanging out of his shell partially but is not attached to anything, his body is almost floating like but the shell is keeping it down.  I added a cucumber for the platys and he hasn't gone near it or moved.  Last I checked he looked like he had a whitish fungus like growth starting on the body portion that was hanging out so I am pretty sure he is dead now too.  When it was obvious he was alive and the fish or frogs would touch him he was move a bit, today when they touch him he doesn't move.  What is causing these snails to die?  Thanks, April

Answer
Sometimes snails are hard to keep in tanks. I know in Petco when we get an order in it's suprising if any are still alive by the end of 2 weeks. We always give them algae wafers, sometimes we've thought the fish had something to do with it. It is really hard to say why they died, I'm sorry it took so long to respond I was in the hospital.