Bala Sharks

[fatguy]

I have kept bala sharks and many other fish for several years. I recently had a very disturbing episode concerning my bala sharks. I have a 150 gallon tank which has a variety of fish including roseline sharks, congo tetra, parrot fish, corydoras catfish, etc. On a recent routine 25% water change all seven of my bala sharks became paralyzed and died. No other fish were affected. I checked the water for pH, hardness and ammonia and the readings were 7.8, 1.0, and 0.0 respectively; as is usual for my tank. I am at a complete loss as to what happened since I make this same water change every two to three weeks. Any help would be greatly appreciated. :?:

[William]

Sounds strange.

Did the water change affect the temperature of the water?

How where the pH, hardness and ammonia before the change?

I would recommend smaller changes more often, perhaps 10-15% every week.