I add 生物石 is mainly for decoration and i dunno know reason behide it.
Well, according to all answer above, i think i will do the following:
1. Keep running the tank WITH the 生物石( i want to keep it) 2. If all fishes are all dead, keep running the water for another 2 weeks at least. 3. change 1/3 to 1/4 water in 4 days.