Snails Dead?

I did a 10% water change last night. That was my first time using water I bought from the fish store. I woke up today and my snails aren't moving. I looked at one on the glass and it wasn't moving, It was perfectly still, except for the power head blowing it around, is it dead?
Levels
Ammonia 0
Nitrates 10
Nitrates 0
Alkalinity 180
pH 8.4