I have a 5 gallon with a betta, and and twice have tried mystery snails. They last 1 month max. They start out vigorous and lively for about a week, then slowly become withdrawn and end up floating most of the time, then dying.
I also do not use a bubbler and have a flow baffle on my HOB. I got a second snail after I started getting a healthy algae growth, and figured the snail might do better on a natural diet. But Cheetoh went the same way as Little Ronnie Jeremy.
I was recently replacing some wood in the tank when I rediscovered that I had made a weight for the wood by silicon-gluing gravel substrate to the aluminum cup from a votive candle. It ain't copper, but it *is* metal...
I'm thinking snails are just not in my future for this tank.
Mooch the Betta (a stomach with fins); 5 gallon planted desktop tank, AC20 HOB with homemade flow baffle.