Dieing/Disappearing Snails

Question
We had 4 small apple snails in our 10 gallon goldfish tank, which they have thrived in for approx. 6-7 months. The 4 medium to small goldfish are all healthy and the filter is working fine, and everything (PH and what not) checks out. However, 3 of our apple snails have "disappeared" leaving only empty shells. The third one that died left a carcass which was rotted and smelly. We are down to one snail and would like to know what happened before purchasing any more.

Answer
Hi Kate,
I've encountered this problem before with apple snails. There are several possible causes to the loss of snails and requires some environmental/care investigation and shell examination of both the lost snails and the living one.

First thing, make sure there is at least an inch or more of open airspace above the water line for the snails to crawl up the sides and take some breaths of air via their special 'breathing tube'.... without this they seem to perish after some time.

Have the snails been fed regularly at night as well? Being in any fishtank, snails are almost always outcompeted for food. Lettuce leaves, zucchini slices, sinking fish foods and algae wafers are much wecome supplements to their usual algae grazing.

Examine the snails shells closely under good lighting. Does the surface look eroded and whitish in places? This is a sign of a weak shell and a too low pH from acidic water due to too much pollution in the tank is often to blame, they need hard water with a decent pH level at least above 7.0 to have healthy strong shells, otherwise, the surface can weaken and cause organ interference and even possible lung collapse. Better nutrition may also be needed.
If you find your aquarium has a low pH oftentimes a simple solution is just to do water changes a little more often to keep the buffering capacity up.
You can also add some crushed coral to your filter to add minerals to help their shells also.

These are the top problems that have come to mind and problems I have also experienced when caring for groups of apple snails.

I hope all is well and best of luck!
Karen~