Sound as if something might have threatened them. Have you seen any blue Herons or any other large animal around the ponds edge that might have threatened or attacked them? If they are trying to hide then that would be my quess. Sandy

Sandy, no blue herons or any other large animals. The koi pond is right up against my house, and the only animals I've seen anywhere near it is a bunny and an armadillo, and of course they're not messing with them. Thanks for your response! All ideas are appreciated.

One other thing. Have you checked your water quality? that might be off. Do a water test and make sure all the reading are correct and that nothin is out of the wack. Poor water quality ususally will effect the larger fish first. check the PH, Nitrites, Nitrates and ammonia, phosphate. I would probably do a 1/4 or more water change and see if that makes a difference. Sandy

I have not checked the water quality. Don't know how to do that but will find out. I do have a UV filter in there that usually keeps it clear, but it does not look as clear right now. I usually cycle the pond - empty water out at the same time adding fresh water, for about 15 min. each day.

I must add, right after you asked about any animals that might be scaring them, I found a small (juvenille) snake in the pond. My neighbor got it out and they seem to be more active, like almost immediately. He said it was a copperhead but I'm not 100% convinced. I am trying to determine what type of snake it was, but it's hard to tell in my snake book and on the net cause they don't always show what the juvenilles look like. I was going to post pics on the reptile forum, but can't figure out how to post pics! :o(