I never had my water tested for metals. It is possible that's an issue for the MTS, but if it was it doesn't bother the pond snails. My grandma is on the same water as me and her tank without fish is filled with so many baby snails. None of my tanks have them to that degree. Anywhere near that. It makes me wonder if fish are part of that. Are freshly hatched pond snails soft enough that a fish could eat them with no problem? I could see my loaches doing that I suppose. I could definitely see the Dario doing it since boredomb had the same shrinking snail population once he got them.
That all might help explain the pond snails, but not the insta-MTS deaths. I'm just a snail killer. After the lights go out tonight maybe I'll shine a flashlight in the tank. I stopped doing that because I thought all the MTS were gone in the 10. If there's one though there could be more. I added them a couple months ago when I added the fish. Each time I added MTS to the 29 they were in their shells when I got them. When i got the ones for the 10 gallon though they were crawling around in the bag and actually active. I had higher hopes because of that.
Boredomb-Sorry forgot to add this before. It's just the Boraras in there which I don't think could scare anything. An adult MTS is actually bigger than they are.