If it really is 8.8, that's a bit high since you could to start seeing odd shell damage. I'm not entirely sure why it happens with apple snails at those pH levels, since it doesn't affect Nerites and MTS, but it seems to be relatively commonly observed in really high pH water with other freshwater snails.
At any rate, if you do need to lower your pH, vinegar will do the trick. Just use it sparingly and carefully and keep a close eye on the kH as well. Using bicarbonate buffers as opposed to carbonate ones can also do the trick, although if your kH is already high those won't work and it's back to something like vinegar. Don't add anything directly to the tank, and experiment on buckets of water beforehand. Once you've figured out how much to add, mix it with a cup of tank water and add slowly into an area of high turbulance (bubbler or filter output)
"That's not a snail...it's a water goat!"--In loving memory of Eatith
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