Mystery Bala Shark deaths

[tbird]

I did a partial water change last week not unlike many times before. I have a 55 g. tank and two of the inhabitants were a couple of Bali Sharks that I've had for quite some time. I had changed about 10 g. of water and everything seemed as usual. The very next day I noticed that the Bali’s were both at one end of the tank and not swimming around like they usually did. I thought it kind of odd but not to the point I felt I should be alarmed. Later that night when I was going to feed the fish in the tank I noticed that one of the Balas was sitting on the bottom of the tank, and then I knew something was wrong. I didn't know what was happening and had the same helpless feeling all aquarium owners have probably felt as they watched an old friend struggle to live. It progressed to the point where it was floating upside down as if it couldn't control its equilibrium. Needless to say it wasn't long before he died.

The other one seemed ok until the next day when the exact same thing happened again as I hopelessly watched it die too. I was and still am at a total loss as to why this happened. Nothing happened to any of the other fish in the tank. I use tap water for water changes, but I always keep some on hand in milk jugs that have set for a week or more. Nothing I did was different than countless times before. Has anyone had this happen to them before or have any idea what could have gone wrong. They weren't at the top of the tank gasping for air like many fish will do if they are in danger of dieing, they just became unable to stay upright and died. Any thoughts would be appreciated.
Thanks.
:confused:

[ewok]

ph, ammonia and nitrite?

always start with the basics when things start going wrong.....

letting the water set for a week does nothing for chloramines either.

check the levels and post back please. if you don't have a kit you can probably get the local fish place to do it for free or a slight fee.

[KateA.]

I would also double check the water you are using and make sure your water conditioners are removing all the bad stuff: chlorine, chloramine, ammonia, nitrites, nitrates.........Anytime you are using a municipal water source you need to check it periodically. They add more of this, less of that, depending on the seasons to make it "safe" for us to drink and we've noticed elevated ammonia and nitrite levels from time to time. And it never hurts to run a pH test before a water change. ;)

[OrionGirl]

Many public utilities are changing over from chlorine to chloramine, as well. If you do not directly receive your water bill, it's possible they sent out notifications that never made it to you (this happened to a friend of mine regarding new watering restrictions--since it went with the bill, and her landlady gets the bill, she never was notified).

Other considerations--any change in feeding? How long it 'quite a while'?

[somefinnfishy]

Any meds? the water is my guess balas are EXTREMELY intolerent of any chems in their water coulum.I saw two of my balas die within 5 min of adding algae killer none of the other fish even noticed.Amonia and nitrites and nitrates most likely arnt the culprets as balas will bang lids and freak if they dont like the water quality and normaly these dont change much overnight in an established tank.

[somefinnfishy]

And BTW welcome to AC:D