New to Snails - tell me things

I just realized that my ph may be the cause for snails in main tank dying off. The ph is in the 6. something range. I have just noticed over a period of time bleached, cracked, abandoned snail shells laying on the substrate. I'm fairly sure nothing in my tank eats snails (cories, angels, tetras and otos). They were hitchhiking snails that I didn't care a whole lot about, but it still is kinda sad. I keep all my other snails in my tap water which is naturally basic and hard.
 
typically you can assume with a ph over 7.5 that the hardness will be adequate. I do not know offhand the exact recommended hardness. The hardness keeps the shells from eroding, while ingested food helps with new shell growth. I have found that feeding the jello and veggies like zucchini are adequate with my water (pH of 8). You can use calcium pills or vacation feeders or wonder shells to help with both. What is the pH of your tank water?

This is a relief, I got a little worried when my pH tested 8.
 
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