:( Our pond snail, in a small aquarium, has been floating at the top of the surface in its shell for over a day. Is it still alive? Do we have to take it out to tell? Will it harm the other snail?
Thanks. :(

What kind of snail is it? How big is it? Is it shut into the shell? Is the shell empty or full (I guess full?)? If the snail has a trapdoor that is shut, that means it is still alive. When snails die, the muscles on their trapdoors relax and open up, often with the body spilling out. You can also do the sniff test. A dead snail will smell really, really bad (not just a little fishy). If it's alive which it sounds like it could be, it shouldn't harm the other snail. If it's dead, then you'd want to remove it to prevent decomposition. If you're not sure, you can put the snail into another container with tank water and re-smell it a few days later and check the trapdoor.

Some snails will float or "play dead" for days or weeks and then recover. My apple snail has been closed up for a few weeks now (but comes out a little now and again so I know he's okay); I just hope he recovers. In my ponds and tanks, most dead snails sink instead of float. The floating occurs if the snail traps air inside its shell and then shuts the trapdoor.