Here are the water parameters according to the test strip:
Nitrate: 20 ppm
Nitrite: 0 ppm
GH: 150 ppm
Chlorine: 0 ppm
KH: 40 ppm
PH: 6.8
Also, the tank has a small sponge filter, a HOB filter, and an air stone. Also a cuttlebone, and I put in a small wondershell yesterday thinking maybe it would help the mystery snail.
There are some plants in the tank and 6 ramshorn tank mates. No fish, but some ramshorn babies (of course!)
I feed the snails invert aquatics mini algae disks every other day.
Thanks again for your help!