Just got a tank setup a week ago. Fish seemed to be doing fine, then did a 25% water change on sunday. On monday, one of the fish was swimming all wierd and looked really weak. He kept resting on the bottom, and would get tossed around by the current. I got worried that the water wasn't right, so I went and bought $40 worth of testing stuff, and the water seemed to be ok.
I did a 50% water change and added the water conditioner...I hope he's ok when I get home today.
(oh, this is one out of 5 fish, the others seem to be ok)