koi in a 300-gallon pond

Question
I have four koi fish.  they live outside all year long.  they got through the winter fine, but all of a sudden one of my koi is laying at the top on a ledge and is very sluggish.  I am really worried.  What could it be??

Answer
I'm sorry about your koi.  How big are the koi?  What else is in the pond?  Have you tested the water (pH, hardness, ammonia, nitrite, nitrate, oxygen)?  Does the koi have other symptoms?  What is the water temperature?  

Koi may act lethargic for any number of reasons including parasites, bacteria, funguses, recent predator attacks, poisoning (chlorine, ammonia, pesticides, etc.), low oxygen, and more.  To narrow it down, we need more information.  

If the koi are large (over a foot), then be sure to check the ammonia and nitrite as they may be too large for the pond.  Koi experts say to have 1000 gallons for the first koi and 100+ gallons beyond that for each addional koi. For three koi, that would be 1200+ gallons or a pond four times larger than the one that you have.  I hope you can build a larger pond!

I also suggest that you contact your local koi club. Sometimes they will be able to come out and check on your pond and koi to determine what is wrong by testing the water, looking at the pond, and putting scrapings of sick koi under a microscope.

Good luck!

Robyn
fishpondinfo.com