I'm very new here and very much an amateur. I don't breed koi, or show them or anything; I just putz around with my backyard pond for relaxation. Have been doing this for about 7 years maybe, but have never seen any of my fish behave the way a few of them are now. Everything was going wonderfully well this year. My pond is about 1500 gallons. Covered about 1/2 in shade. Water is in good condition. Various small-to-medium koi and goldfish (24?). New filter installed 1 week ago- great water flow. All fish doing great all season. Added 4 new koi 1 week ago also. The new ones adapted very quickly and everything was fine up until yesterday afternoon.
I'm not even sure if this is a "problem" per se, but I am worried. As of last evening, some fish have taken to just settling on the bottom of the pond- sometimes in the deep end, sometimes in the shallower areas. (So I don't think they're trying to get away from any predators.) One has even completely buried himself in between some rocks. The thing is, when food is offered, they will come to eat normally, and be active, but then go right back to laying motionless. (The buried one does not come out anymore). The ones that are laying are, for the most part, the new ones added last week- but there are one or two others who are showing this same behavior.
If anyone has any input into this, I would be very grateful.