I was away for 10 days during the Chinese New Year holiday and found all electrical appliances were turned off due to a circuit overload or some sort when I returned.
All fishes in my FO tank died and turned rotten.Since I was running out of salt so I took out as much water as I could (just above the sand) and put in fresh water to dilute the toxic matters that may have accumulated.
A complete water change again the next day when I brought the salt.
My question is will the 硝化細菌 be destroyed in this circumstance?
THanks.

If you put in fresh water to dilute toxic matter and put all fres water in the tank over 12 hours, I am afreid that all bacteria sys. in your tank were distroyed.

yes.....if you really use "fresh"water