Koi & Pond Fish

A crash course in starting out with pond and fish for the basic noob.

The Top Ten Things You Need To Know and Master For Success With a Koi Pond

The Super Basics

Figures out all the following:
Inventories quality, informational resources for a deeper understanding

But the most successful garden-variety hobbyist:
Feeds decent food, redundantly supplies their pond electrical, supports lively water movement and intercepts temperature impacts, knows their water’s quality via periodic basic water testing with strips, feeds sparingly and never gets new fish. Removes excess fish each year and avoids any drastic changes in population or water. If new fish are in the plan, quarantines new fish before deploying.

1. Crowding

You should have one inch of fish per ten gallons of pond water. You can have a bunch more fish than that IF the filtration and water quality will support them. To calculate pond volume figure out approximate length, width and depth in inches. Multiply them thusly:   Length inches x Width inches x Depth inches = Product    then divide the product by 231 and there you have US Gallons. If you have a mess of small fish, like goldfish and under 6″ you can have a lot more than an inch of fish per ten gallons. But the larger fish have more “mass” and oxygen requirements and put out more wastes and so they push the number down to one inch per ten gallons.


2. New Fish
The main source of parasites / germs is new fish. For the most part, “closed collections” don’t get parasites as a “new thing”. To avoid parasites and even some germ infections, quarantine is imperative which stymies the pathological “impulse buyer” but you know, live with your decisions.


3. Their water:

Water Movement is probably the most important thing in a pond. Most of the time when fish have poor body language, clamping and lethargic, it’s a lack of aeration and water movement in warm weather. How much water movement is needed?
Aeration is the single most important parameter with a close second being pH because of ‘crash’
Another area NOT to be ignorant of is water chemistry. Seriously. Flying blind is just ignorant unless your collection of fish is entirely expendable. MOST people have their fish and pond problems from chemistry, especially pH.

Chemicals like pH, and nitrogen.

Nitrogen is represented by Ammonia, Nitrite, and Nitrate. You should understand the basics of all of these. You’re not going to do “okay” for very long without understanding how Nitrate comes back to bite you in the butt. It’s the SINGLE MOST COMMON cause of chronic illness in the ponds of “know it all” pond and Koi keepers. They do a LOT correctly except they make VAST assumptions about their water quality because they think they can eyeball water quality.

Ammonia Discussed: When it happens, looks like, what to do.  (Video)

Nitrite Discussed: When it happens, looks like, what to do. 

Nitrate Discussed: When it happens, looks like, what to do. 

pH and pH crash are perhaps the most common water “quality” problem. Newbies won’t succeed long without a handle on this. Link to Video.

New Water

Water needs to be turned over and replaced with new water from time to time. At LEAST 10% per week. I run a constant slow water drip all the time. That’s because I’m lazy and don’t like to change water. Topping off the pond is not a water change unless the pond leaks. Evaporation CONCENTRATES chemistry. Doesn’t dilute it. When you replace water “fill and drain style” you need to apply a chemical “dechlorinator” to neutralize caustic chlorine that’s added to city water to disinfect it. If you’re using well water it’s not a “thing” but you might check the pH of the well water to know if it’s low.

Well water video

Dechlor video

Pond location and impact of temperature

If your pond is in the shade then it might get lots of leaves in it. And if it does, those leaves will decay and reduce the pH. If the water gets stained a “tea color” with leaf tannins (from leaves on and off the tree interestingly) the tea colored water will usually have a low pH, will slow healing of wounds in the Spring, and never grow algae. Tannins are anti-algae.

A pond in full sun  is prone to algae blooms, won’t have leaves in it, will not have much in the way of leaf-pH dynamic. But the water will be warmer and WARM WATER carries less oxygen so water movement and aeration are critical. If water movement fails in the hot pond in mid summer because, say, power outage, the fish are gonna die.

4. Their filtration:

So when you start out or you inherit a pond, the “filter” might sound simple but usually it’s not. They need maintenance of some kind. And they may or may not be “big enough” and an assessment is needed. I use ecosystem ponds with plants and gravel and a waterfall, happily. It takes MAJOR maintenance on the yearly. I also run some systems on Bead Filters which pass the water through beads to clean it. VERY easy to clean, but they can jam up suddenly, die in the sun if the power goes out, and are a little expensive.

In any event, you should learn about filtration in earnest. For the beginner, an ecosystem installation or a bead filter would be your two best, scalable options. Cleanliness and maintenance of said filtration and water are paramount. Get educated by a knowledgeable installer or retailer of filters.

Ecosystem ponds

Excellent bead filtration I

Excellent bead filtration II

When filtration is needed or not 

Well if the pond is large and the fish load is small, you probably won’t need a filter. If there’s a lot of water movement and the water is clear and there’s not a bunch of cloudiness or particulate clouding, you might not need a filter. If the water tests okay with dip tests, you might not need a filter.

5. Their feeding

Overfeeding is super common. Just don’t. Koi do best when you have a ten year old feeding them and they forget to feed every fourth day or so. Underfeeding is better than overfeeding. If your koi are fat, something’s wrong and your water quality is probably paying a price. Fat koi are just fine. Feed twice a day, tops. Feed what they wanna eat in under ten minutes. Five minutes would be even better. Don’t feed near the skimmer or it’ll take the food and give it to the filter unnecessarily.

What to feed.  Feeding the right food is pretty important but really, in the scheme of things, it’s uncommon for a poor food choice to kill or sicken fish. Even catfish chow (while really inadequate) will just result in fatty livers and increased vulnerability to disease, not kill them.  Here’s where to learn all about Koi foods, and even some recommendations.

When Not to Feed and Why. So if your pond is large, natural and has ecosystem forage (plants, tadpoles, swimmy bugs, stuff like that, and the fish load is light, you might not need to feed. If the pond is a tech-pond without plants nor gravel you need to feed. There’s no natural forage.

6. Fish Body Language

Fish body language is just an Early warning system for disease or poor water quality.

Here are some pointers:

  • If the fish are moving around, curious about food they’re probably okay
  • If the fish are NOT using their pectoral fins (the ones behind the head) they’re sick.
  • If the fish are wagging their bodies to swim, and not using fins at all, they’re about to die.
  • If the fish have clamped fins but then swim normally when you show up, something’s going on. Like a too high temperature or a sagging pH.

Survival is suggested by at least some willingness to eat, moving around.
Body wag is probably a goner.

7. Parasites

Where they come from? Parasites CAN “just happen” and they can be “carried” for a long time without causing disease until Winter reduces the fish’s immune system. Or, more commonly, parasites are not a “thing” until you buy some WITH PARASITES already on them. Quarantine fixes and prevents that. It’s easier to treat in quarantine and keeps your existing fish safe. VIDEO ON QUARANTINE

How’d you know they had them? Poor body language is an indicator something’s not right. Usually that’s a sagging pH and or a low dissolved oxygen. But if those two aren’t going on, maybe parasites are a “thing”. Fish will scratch on tank / pond surfaces and rocks, like “flashing” and they’ll also show up with red skin, red veins in their fins, stop eating and develop a slimy skin. (All those symptoms happen in pH crash, too)

-Water quality is 3 to 1 over parasites for the source of illness. Yes and that’s annoying. People OFTEN contact me and ask what medicine to use for this or that symptom they’re seeing. Or the medicine isn’t working. The fish gets worse. So I ask them what the pH is. What the Ammonia is. What the Nitrate is. And they get back to me with a number WAY out of range, fix that, and no medicine was even needed.

What you can do: A video introduction to the major categories of parasites and some treatments worth knowing.

8. Bacterial Infections – Rot

What sores mean:  Sores just mean the fish have “gone through something” that broke their immune system. Cold water, over crowding, high nitrogen levels, a low pH, wintertime, low dissolved oxygen, cold water, excess handling and parasites chewing on the skin are all very common causes. Just exposure to bacteria (even the baddest of the bad) don’t CAUSE bacterial infections.
What you can do: You have to diagnose what happened, what “they went through” and then fix that. Provide an optimal environment. And then perhaps apply antimicrobial treatments to the water, in the food, by injection. Literally everything you would NEED to know in order to deal with bacterial infections is at my Koivet Youtube page. But also

Ulcer Disease I, II, III

What you can probably not do: You can’t save fish that are:
-Too far gone
-You may not be able to obtain or give injections of antibiotics but they work great. Perhaps you could find a vet that can help. Injections for really valuable ones
Water treatments for other cases like Potassium permanganate or Chloramine T.

9. Viral Infections

What viruses are there, in general: If you don’t get more fish, viruses aren’t a “thing” for you to worry about. But there are viruses out there which will kill almost all your fish. The main one is Koi Herpes Virus. It depends on water temperatures to kill fish. Under 70 degrees Fahrenheit, it’s inactive. Above 80 degrees Fahrenheit, it dies off. Fish are saved. If you quarantine fish according to the video mentioned above, and the fish achieve a temperature in the low eighties, Koi Herpes Virus is a non-issue.
Other viruses include viruses that cause warts, little waxy droplets on the skin, and are not lethal. Spring Viremia of Carp is a common disease that appears to be endemic (in everything) to north America and causes depression of the immune system potentiating bacterial infections. You wouldn’t know if your fish had this, because if you test for it, you’re likely to get a positive, and then you will have your pond closed, killed off, and quarantined.

10. Shutting down for winter

When not to feed:  Koi and pond fish do better in very cold water WITHOUT food in their tracts. It’s a good idea to suspend feeding when the water temperatures sail down below 55 DF — IF you can anticipate the temperatures are going to decline FURTHER like a typical temperate climate. (North American near freezing) – However in Portland and other geography, the ponds might hit 55 and NOT go down, so those aren’t “heading to icy” and so if the temperatures are going to hover above 40 DF you should feed Cheerios.

When to shut down the filters?   You can keep your filters running unless it’s going to freeze and you have to “winterize” the filters, so you ought to talk to your installer or filtration manufacturer about how to deal with temperatures prevailing in your area. If your filter has a return under water or which won’t super cool the pond, you can leave it on. The biological activity of the filter will be sadly lacking so feed less, or feed Cheerios.

How to turn water over
-When you don’t really have to:   When water is in the low forties and lower, it carries all the oxygen it can. So water movement isn’t a “thing” at that point. I mean, SOME water movement is important but that’s mainly for gas release (CO2 etc) rather than Oxygenation.
-Striking the ice –  It is a myth that if you strike the ice over pond fish, they will die or go deaf. In fact, sometimes fish die under the ice and that had NOTHING to do with someone breaking the ice. Usually it’s the fact that they even HAD to break ice. Ice need to have a hole or gas exchange gap in the surface. If you have to use a floating cattle trouble heater, do it.
-What Springtime means: Springtime is tough on Koi and pond fish because typically:

  • The fish have gone hungry all winter
  • The fish have been cold and their immune system is warmth-fired.
  • Parasites don’t care if it’s cold and can strike in cold water with extra vengeance.
  • Water bacteria (purification bacteria) are largely dormant so water quality is at it’s lowest.
  • A winter’s worth of fish excreta and plant material / last year’s mulm are all suspended in time, and break down as soon as water temps rise. It’s a surge in algae / bacterial nutrition.

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