What could cause a nerite snail's death?

[Aqua315]

Hi everyone! I recently lost one of my 3 nerite snails in my 28g tank and am really confused as to what caused it. The snails have been in my tank for a few months now and everything seemed fine. My current stock is 8 neon tetras, 2 gold barbs, 4 albino cherry barbs, 3 otos, and (now) 2 nerite snails. All my parameters are normal. Ammo:0 NO2:0 NO3:35 and I hadn't noticed anything out of the ordinary. A few days before I noticed he was dead I saw him on his back. This had happened before so I didn't think much of it and just flipped him over. He didn't move much but I know this can be normal for a snail sometimes. A few days later I noticed he hadn't moved in while so I picked him up to be sure and one sniff told me he was definitely dead. I've made a lot of mistakes with fish tanks before and I'm trying really hard to take care of this one really well. I'm just confused as to what could have caused this.

 

[Nomadu571]

Age? Just his time to go? Did you supplement their diet with wafers or somthing, if there wasn't tons of algae for all three?

Unless he was eaten by somthing I don't think there much that can be done. Hopefully it's not catching, if the perams are normal, these not much that can cause it.