ID snail please

kona

Member
About 1 hour after the lights in my tank turn out, at least 30 snails come out of hiding and cover the inside of the tank. During the day, I rarely see these guys, but, after the lights are out, they all come out.
They are about 4mm in diameter. Are they detrimental/good for the tank? Do I have to worry about overpopulation? Incompatibility? Thanks.
 
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