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Raising Koi: Facts and Myths


Todd Williams shared his deep thoughts on caring for koi.

Myths and half-truths. They are everywhere. Only humans can take a small nugget of truth and twist it into something entirely different. And we all like rules-of-thumb. They help us simplify a world with lots of information. But these can get out of hand. I find this to be true with koi ponds. I’ve compiled a list of frequently stated “facts.”

-Ponds can hold a max of 1″ of koi per 100 gallons

Not only is a rule for this misleading but using inches over weight is ridiculous. How can four of my 6″ inch fish possibly equal a 24″? The latter’s weight is 500% more! But it gets worse: even if you used pounds, there are simply too many other factors to have a rule-of-thumb on this topic. We’ve all seen ponds twice as big as your own that can only handle half the fish. Things like pond water turn-over, proper balance, filtration, number of plants and type of plants all matter.
Bottom line: I say just don’t use any rule of thumb on this topic.
Conclusion: Myth.

-How fast do koi grow?

Once again I think it’s misleading to even give a number. It seems that most koi experts presume you live in the warmer half of the U.S. But why? I live only a few miles from the Canadian border. My pond water is only above 70 degrees for maybe 10-12 weeks a year. That is when koi eat more and grow more. I’ve been surprised pond people don’t simply give answers to this legit question using regions i.e. plant zones.
Conclusion: Half Truth only if you qualify the answer by zone. But even then there are variables for growth.

-Stop feeding koi after five minutes

Say what? This reminds me of people who are concerned about burning their plants from watering them. I’ve seen people not water their yard for days when it’s hot, thinking water would do more harm than good. Think of it like a baby. They eat slowly. Some more slowly than others. I must admit I can’t back this one up with any science except this just does not make intuitive sense. On one website it says “whatever food is uneaten after five minutes will likely not get eaten.” That is true! On another website it says “Don’t feed them for more than five minutes.” Mmmm. Did a fact get twisted into a myth? If you have time, it’s quite OK to let your koi nibble over time. Like a baby, you can tell when they get satisfied. Conclusion: Myth.

-Don’t ever ever ever put your hose directly in the pond.
It’s assumed that chlorine could kill the fish, and it’s best to have the water spray in the air and “release” the chlorine gasses. I am certainly no chemist. But this never totally added up to me (and I have a pool so the whole chlorine thing is not new to me). In my town the water report says we have 6 chlorine parts-per-million immediately after water processed. People get confused by large numbers. How long would it take you to count to a million using one second per number? Over 11 days! Six seconds of chlorine over 11 days isn’t hurting anything. But, for the sake of discussion let’s say 6 ppm is harmful. It never made sense to me that letting the water “hit air” for literally one second would make the water safer. Guess what? It doesn’t. To verify I called my local water treatment plant. This guy’s job is to process and test city water. I told him the rule of thumb. His response makes perfectly logical sense. He said “Chlorine does dissipate with time. However, tossing a cup of water in the air will not make the PPM-count lower by time it comes down.”

If filling up a pond from scratch, it would be 100 times more important to wait a day or two before adding fish than to have the hose not be in direct contact with the water. Meaning, aquarium people are correct to let water sit out for a day if they are doing a complete water change. If you are topping off your pond, go ahead and better be safe than sorry. Leave the hose out. But your concern would be much better served by checking chemicals regularly. And to add an interesting twist. My pool repair guy always reminds me to not put the hose directly in the pool. And in a pool we want chlorine. Why? Because you can easily forget and leave the hose running in the pool overnight causing many problems. But when you leave the hose out and have it splash in, you have a much better chance of hearing or seeing the water, thus avoiding a problem. Conclusion: True on hose rule, but a myth on the reason why.

-Koi food left in pond is same as fish waste.

Let’s just say that is silly. What goes in a cow is certainly not what comes out. Think of it another way; koi food does not give plants nutrients. Fish waste does.
Conclusion: Myth.

So enjoy your pond. And next time someone states a fact, it’s OK to “ponder” if it’s really true.
Todd is a hobbyist with pond-grade koi. He (barely) got C’s in science. But he does think about a lot of things while enjoying his pond. He was considering a Twitter campaign of #StopKoiMythsNow. But his family threatened to kidnap his koi if he did.

date Posted on: Wednesday, June 4th, 2014 at 2:57 pm
Category Pond News.
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  • Margaret Poole

    I like your advice.

    I live in SW Michigan and have had many Koi in my ponds since 2006. We keep the water running and have floating ice-melters in all 3 ponds. We were heartbroken this spring after the big melt, to find that every single Koi had died. We can only attribute it to the extremely harsh winter.

  • Roberta

    Please verify these are myth or true:

    1. Well water is not oxygenated enough and should be “lofted” into the pond for oxygenation when refilling.

    2. Baby koi live on Algae in the water so a totally algae-proof pond isn’t good.

  • http://karinbarrett.rein.fusionmls.com Karin Barrett

    My large orange koi, has on her side no color. It looks like it was cut off. She is swims slow, but loves the air bubbles released from the bottom. Can you let me know what I can do to help her and what may have caused the problem.

  • http://www.pondpro2000.com Niocle Martin

    Pond liner by Pondpro2000 is essential material to shield pond from spillage. It ought to be ultra rough resistance with the goal that sun beams can’t create breaks or little gap in pond liner.