水草情迷

How come all my "sun" snails have died or are dying?

My tank is-
1) DIY co2 one bubble / 2 sec
2) 30 L tank using Ex90
3) 2" Ada soil without "foundation nutrient"
4) 40 small fishes
5) T5 8w x 4 tubes (32W) turn on for 10hrs daily.

What are the problems??