I can't believe (after reading this thead and thinking, "oh no, bad mistake!") I did this very same thing overnight! I woke up at 5:00 am today to the slight sound of water running. Panic! I'd put the hose in the pond at 6:00 last night. Ran out, shut off the water, came in and rumagged throught the "fish stuff" cabinet to find enough dechlorinator to treat just 1/10 the volume of my pond, which I dumped in in the darkness.
When it became light enough, I went out to find all my fishes on the bottom, not swimming around, but alive. I have a fish supply store one minute from my house, but they don't open until 10:00!
At 10:00 I was in the store, and out in a couple of minutes with enough dechlorinator. Flew home, measured, dumped. By then it was bright and sunny, but all the fish were still on the bottom, when normally they would be up and about begging for food.
Wait and watch....by 1:00, they were starting to move! 2:30 came around, and most of them had made it close to the surface. I put a little food in, which they barely noticed.
Right now it's 4:15 pm, and I just checked on the pond. The fish are all up and about, but are still not 100% active. I tossed in a bit of food, and each of them seemed to get a bite, but not beg for more. Bet they are not feeling very good yet. It's still not over, but I now think that this will have a happy ending.
I have had this pond for 11 years, and never have I let this mistake happen before. From now on, a timer will be set, and my smart daughter suggested that I lay the hose across my front steps so I have to trip over it to get back into the house. This could work for others, depending on your house/hose/pond location!
Thanks for listening, I've been stressing out over this and got long-winded!
Diane