I have had 4 snails, and within a month or so, two of them died. We thought that we were putting too much salt in the tank, so we put in less. When I found my two snails had passed, I had noticed that one was still active, but a little less than normal. So, I put her into a smaller tank in my room. She seemed very pleased and much more active with this. Then, about 5-7 days later, she passed. Now, my last snail, Lizzi, we think she has passed, because she has not been active for about 4 days, and I know that they hibernate, but when I took her out to see if she was still tucked into her shell, she had a little bit of a odor. (Like rotting) We are going to give her until tomorrow, though we pretty much know she has passed... I have had apple snails in the past, one of which lived to be about 2 years old and a good size. I was just wondering if this could be the high amonia levels in my tank, though we have not tested for it we are assuming they are high, because I have 3 goldfish, 2 of which are about 3-3.5" and one that is about 11". I also have two dojo loaches in my tank that are full sized. Could my snails have passed from the amonia levels caused by the goldfish, or is it something else?

Wait...salt? Thats your first problem. You should never under any circumstances use salt when theres snails in the tank. Same with loaches...NO SALT. Can you answer these questions for me please?

How big is your tank?

Which variety of apple snail do you have and what are you feeding them?

Whats the water temperature?

Can you get your water tested to find out the levels of ammonia, nitrite and nitrate? If your tank is cycles ammonia shouldn't be the problem...if it isn't your snails could be having troubles with ammonia.