Koi in Aquarium

Question
Hello.
I have been keeping goldfish in an aquarium for several years, but after they died, I decided to move on to a different breed of coldwater fish. I was wondering if I could keep my single koi in my 20 gallon tanks for his whole lifetime. (So far, he is only a half inch, and since he was born and bred from pet shop tanked koi, I figured it should be ok.) There is nothing else in the tank, besides a couple of silk plants, a log, gravel, and a snail I will remove soon, because the fish has already attempted to eat him twice. Also, I've got 2 powerfilters, providing about 50 gallons an hour of filtration. Would this be ok?

Also, all my new koi seems to be doing is having random bursts of hyperness. He would be drifting calmly around the tank and then suddenly zooms around, with no apparent signal. He dislikes eating the floating koi pellets I got from the store also. Would he be able to get used to them? I have a feeling that the pet store only fed flakes.
Thanks

Answer
Hi Sunny,
Koi fish get real big and should be in ponds or big aquariums.  Small tanks will stunt its growth and will cause it to develop health problems further down the road.  A lot of people say fish dont outgrow tanks and its ok but they dont know that fish that "dont outgrow" their tanks is because their growth has been stunted.  Your filtration and setup is real nice but a bigger tank will be needed once he is bigger.  Koi usually eat any flakes and pellets.  He might not be used to it.  Or is currently still adapting to your current tank.  Once he settles in, everything should be fine.
-Matt-