Hey! The fact that she did lose koi last summer is troubling. A pond loses koi when it is overstocked. What kind of aeration does the pond have? Waterfall? Fountain? How deep is the pond? Roughly what shape is it? I want to calculate the gallons and see if there would be room for one more fish.
Also what does the bottom of the pond look like? Is it filled with leaves and mulm or can you see rock? Does she have any plants in the pond? Sorry for all the questions. I'm trying to get a picture of the pond in my head. Although if you have a photo of it that would also be wonderful.

Hi Izzy. I spoke with my friend who I intended to give my baby koi to in the spring and now I'm a bit worried. It sounds like her pond may be too small and shallow. It's roughly 10' X 8' and has 9 koi who are each about 1'. I do know that she had more koi but some died last summer because the pond was not deep enough (possibly not enough oxygen and no aeration provided). What is your opinion on this pond? I'd really appreciate your advice.

With those outdoor temps, you are right to keep him in a tank for the winter. I'm glad to help. Koi are wonderful fish that live longer than some of our furry friends. I hope you'll be able to watch him grow and blossom in your friend's pond. Also he has an adorable name.

Oh, sorry I was unclear. No, I meant that if I needed to rehome him in the pond right away, those would be the outdoor temps that he'd have to adjust to as opposed to the indoor temp he has now, which has been a steady 70 F but will now be lowered significantly.

Thank you so much for all your advice and for sharing your knowledge. Koichiro and I greatly appreciate it. :)

Would it be better if I tried to rehome him now? The lowest it gets is about 30 F at night, maybe 50-60's during the day.

Oh, he's cold all right. :) His tank is in the garage, so it gets down to 65 F or lower. I'm keeping him at 70, should I lower it?

They really grow that fast?

Your situation is a tough call. For what he is in right now, he is fine. But the problem is those little buggers grow like crazy. Can you keep the tank in the coldest part of your house? His growth will slow that way.

So I'm reading your posts for LyzzaRyzz's koi dilemma and now I'm curious about your opinion on my situation. One 4" baby koi in an overfiltered 37g until the spring. He'll then be rehomed; I already have someone with a koi pond who wants him. I was told not to rehome him during the winter because the shock could kill him so will he be okay in the 37g until about March or April? Otherwise, I'll see if she'll take him now.