Question
Hi.  My pond is 1500 gallons,and has ten koi carp.the last two i brought were purchased in June 04,and both were the same size(approx 15cm long).  One koi has grown to approx (35cm long),but the other one which is an orange metalic colour has only grown to approx(20cm long).This does not really bother me as the fish always seemed healthy.Over the past week or so this koi has seemed lethargic,moves slowly in the water ,and does not seem interested in feeding.It very often lays on the bottom of the pond near the pump,and just lately it has taken to resting near the surface(on the level platform where i place my plants).Today I saw it lying in this position,and I was able to go up to it and stroke it(normally all my koi would dart away if approached).   A couple of days ago the koi was in the same position but was lying on its side ,and I thought it was dead.It swam away slowly when approached.  Advice would be appreciated.

   Thanks  

Answer
It sounds like the koi is ill.  First, rule out water quality issues.  Test your water for pH, hardness, alkalinity, salinity, oxygen, ammonia, nitrite, and nitrate if you can.  With so many koi in your pond, I wouldn't be surprised if the ammonia or nitrite were high even though the fish are small, especially if the pond is new (how old is it?).  I only have two koi in my 1800 gallon pond.  It's also not a bad idea to test for heavy metals.  If you have city water or not, add some dechlorinator because it will neutralize both the chlorine in city water and heavy metals.  Koi are pretty sensitive to heavy metals.  Do a 10% water change with dechlorinator and pond salt added.  I suggest 0.05% salt if you have plants and 0.1% if you don't.  Salt helps with many problems including parasites, bacteria, and high nitrite.  Be sure the filters are clean and put in some fresh carbon to remove any toxins you may not be able to test for.  Be sure the water is well aerated.

After ruling out water issues, check for parasites.  I just took a class on scarping for parasites.  If you can't do it yourself, contact your local koi club.  They normally do it for free.

If the problem is not the water or parasites, it may be bacterial, fungal, or viral.  Bacterial is most common.  You can try natural MelaFix right in the pond or treat the sick koi with antibiotics in a quarantine pond.  For internal infections, injections of antibiotics can be done but you'd need to find a vet to supply the antibiotics.

The lady who taught this class I went to yesterday also takes in live (until she kills it) or dead koi to diagnose them and also can do water tests.  The cost is $38 for either but shipping for a fish can be a lot.  If you want me to find her web site, let me know.

Also, check out http://www.koivet.com
They have a forum and can answer koi-specific questions in more depth there.

Good luck!
My site is http://www.fishpondinfo.com/pond.htm and has sections on health and koi but not too much.