Welcome to ponding and the ponding newsgroup. You will probably get
quite a few posts from people telling you that your pond is
overstocked. I find that everywhere you go you will hear a differen't
answer. Some will be nicer than others also . From this
newsgroup...you've heard it already.

Now my opinion, from my experience. I have kept 4 - 5 koi in a 220
gallon for years without trouble. The oldest koi I have had made it
to his 16th summer. What I have learned from personal experience is
that less koi per gallon and overall having more gallons to begin with
make keeping the pond easier. There is less filter cleaning, less
waterchanges and much less trouble with alage. Your pond is descent
size for your fish for now... keep the filter clean, keep lots of
plants, pray to the pond god... and have patience when you deal with
water condition fluctuations that can come with having more fish. My
biggest was always algae.

FYI, Currently, I hava a 220 gallon pond for new fish 2 years old
and I have a 1250 - 1350 gallon pond for my other koi (these past few
weeks near 100 degrees evaporate a ton of water). BTW, I currently
hav 11 koi-- bought some more babies yesterday... they looked at me
with the big eyes they have, I couldn't resist.

You may already know that koi grow fast. The 4 babies I bought about
2 months ago and they have outgrown my feeder goldfish that are 3
years old. If yours get too big... you just have justification for a
larger pond

Good luck.