I think you may have just answered some of your question about why your snail died.its all ppm, the alk rn, I don't really care about, since im still cycling
If you're still cycling, livestock will not typically do well due to the elevated levels.
Regardless of cycling. Your alk shouldn't be swinging like that. It is anything but stable. If true. I don't think it's true though unless you're doing a lot of water changes between tests.
What are you using to measure? You should make sure you're following instructions and take time to practice the test. Alk doesn't matter until you have corals, but use the time now to practice test methid.