Looks like fish might be dying, please help

Question
Hi, I have a tropical tank with a small finrot issue.  Today I changed 25% of the water and added the relevant treatment for finrot and water treatment, but since doing the change/treatment alot of the fish are swimming upside down, lying upside down on the bottom, lying against where the water filter goes is and in particular my clown loaches and some larger fish are just lying on the bottom looking as though they are dying (the clown loaches do this regularly I know, but normally move if you go near the tank - on this occasion they look like they are gasping and cannot move).  Also one of the clown loaches appears to be gasping at the top and banging into the tank swimming upside down.  Have you got any ideas what has happened?  I'm desparate as I don't want all my fish to die.

Answer
They sound like they are shocked.  There was something wrong with the water you added, too hot or cold, forgot to de-chlorinate, maybe.  Generally when you are treating a tank, you don't change the water until after the medication has been in the tank a few day.  It's really hard for me to say what is going on, there isn't quiet enough info.  How big is your tank? What fish do you have other then the loach? Have you had your water tested? What meds are you using?