This is a discussion on What's wrong with King Snail? within the Invertebrates forums, part of the Freshwater and Tropical Fish category; -->
For the past hour my only remaining GAS has been out of his sheell more than usual, not moving from the spot he's on, ...
A snail laying in this position for a long period of time usually has poisoning of some kind. Your tank params look ok though. Any fish meds in the tank? Untreated tap water? Take your snail out of the tank right away for 15 minutes so he can have a breather and dose your entire tank with water conditioner. It's possible your water supply has more chloramines or something in it that it usually has. Please post an update.
I'll know for next time thoguh I'm still not sure because it was for my tank which has only the betta and snail, and bettas are sensitive to this medication so I quartered the recommended dose for him anyway.
When I came back my holiday a fortnight ago the tank had high amonia and nitrite which killed the other 3 snails. I quickly got the params back to normal and put him bak in the tank so I thoguht he'd have been fine. Is it possiby in your opinion that this was just a delayed reaction or something?
I think it would be very unusual for your snail to succumb at this late date unless you've seen a gradual decline in him. It sounds like it was a pretty sudden thing.
For the future, if you ever notice unusual behavior, take your snails out immediately and test your water. It is within normal behavior to float or sit closed up on the bottom for a day or two. Be very careful with medication, though I still don't think it was the Melafix. Anything that isn't safe for invertebrates needs to be avoided. If you're at all unsure, take the snails out until treatment is completed, charcoal used, and water changes are done. The great thing (well, one of the great things) about snails is that they can easily live in a rubbermaid container with frequent water changes until the tank is safe for them.
There was no gradual decline! He was fine in the morning and when I came home from work he was like in the photos so I tested the water and the results were as posted. I really can't think what might have caused it however in future I won't leave them in the tank if anything happens, I'll take them out and wait for them to get better.
I know this doesn't help now but looking at the picture it looks like he might have had a calcium deficiency. I had the same problem and had the same look with my golden mystery snails before I started adding lots of calcium and crushed coral to the snail tank. I also lost them in about the same way you did. They would simply drop to the bottom one day and die in less than 24 hours.
First is to find a calcium suppliment, I use Calcium Citrate powder from a Health food store in powder form. I dose a heaping 1/4 tsp every other day.
Second, I have started to notice that they really prefer and more important need veggies to be healthy. I had gotten my first egg clutch about a month ago and then nothing. Could not figure out what was different. Then I realized it had been about that long since I gave them green beans so I gave them green beans yesterday and the day before and low and behold, another clutch today. I could be way off base but it seems to have made a difference. It has also seemed to help with the bloated look both of them had and what might have actually killed the one that died the other day.
Just a side note, as Trish has told me, they don't live all that long, 2-4 years, and who knows how old they are when we get them from the LFS. I know the ones that are offered from my LFS are in pretty bad shape and are a challenge to get them to survive.
How do you get them to eat leafy greens? Mine won't touch them, none of them! My Colombian Ramshorns lived off of Romaine but I put it in there for my mysteries and it sits there. Not even the ponds snails nor common ramshorns will touch it. I wish they did because I really want to get rid of most if not all of the pond snails becaus eI simply hate them now. Acutally thinking of taking my ramshorns and mysteries out again and changing tanks with my loaches again.