Top Ten Ways to Kill Your Fish
Koi and goldfish are both fairly hardy species, but there are a few sure-fire ways to eliminate all life in your pond.  
Please be advised that just because you know what these ways are doesn't mean you won't do at least one of them
over the course of pond ownership.
Go Back to
Home Page
Our Ponds
Koi Shows
About Us
About Us
DIY Hints
The number one, numero uno, top of the list, sure-fire way to kill your fish is (drum roll please . . . . . . )
with the garden hose.  That's right.  That innocuous little rubber tube that gives life to your flowers and shrubs can
be lethal to your fish.  It will only take you one time to forget to turn the hose off after topping the pond up or a
water change to wipe out everything you hold dear.   The reason is that cities treat the water that you and I drink
with chloramines (chlorine and ammonia), and both are toxic to fish.  The combination of chlorine and ammonia can
also be toxic to humans if the two are combined in an enclosed environment, like a bathroom.  The fumes created by
mixing the two will burn the lungs, causing the individual to pass out and can ultimately lead to death.  The same is
true for your fish.  Chloramines burn the fine, feather-like gills of the fish, making normal respiration difficult and
labored.  If you catch the problem in time, you may be able to save some of your fish by immediately treating the
water with a chloramine binding agent like AmQuel or Chlor-A-Max, but the gills of the fish will be forever scarred,
making the fish weaker and less likely to live to it's full life span expectancy.
Second on our top ten list is suffocation.  Fish need air to breathe, just like we do, only they breathe a little differently
because their whole lives are spent under water, not just the first 9 months.  Suffocation occurs when there is not
enough dissolved oxygen in the water to support the volume of life present in the system.  Since the bigger fish
require more oxygen to survive, they will be the first to go, first gasping at the surface to try to get more oxygen
through their gills and ultimately dieing.  Suffocation can be caused by a number of things.  Inadequate water
circulation is just one possibility.  A pond that is too shallow heats up more quickly than a pond that is deeper, and
water holds exponentially less oxygen per volume as the water temperature rises.  Tannins and dissolved organic
waste in your pond can also reduce the oxygen levels to an unsafe level.  Additionally, submerged plants, which
during the day convert carbon dioxide to oxygen, reverse the process at night, converting oxygen to carbon dioxide.  
In heavily over-planted ponds, often in combination with shallow ponds, this can become lethal.  Certainly
overpopulation is another key factor in the oxygen equation, and having to many fish for your volume of water will
put your fish under undue stress, causing a number of ailments, suffocation being just one.
Number three on our list is a pH crash.  Although it is VERY unlikely in our area (Central Illinois) for anyone to
experience a pH crash in their pond, it is a problem in many areas of the country, hence the reason it's number
three.  A perfect pH is 7.0, however, the pH in this area is pretty constant at anywhere from 8.5 to 9.0.  The fish will
adjust to this higher pH with little problem, as long as it remains constant.  The reason we here in Central Illinois
have very little fluctuation in our pH is because we have a very high (almost off the charts) KH, or Carbonate
Hardness.  KH, or Carbonate Hardness, in laymens terms is the dissolved mineral content in the water, and our water
is very hard.  KH stabilizes pH levels.  The fish need an adequate level of KH to survive, as they absorb the dissolved
minerals in the water through their skin.  In areas where the KH is low, a heavy fish load, or infrequent water
changes can cause the KH to get used up, and when that happens, you will experience a pH crash.  If the KH levels
in your area are questionable, the best thing for you to do is to add crushed oyster shells to your filter system.  As
the KH in the pond gets used up by the fish, the oyster shells will dissolve to replenish the KH supply.  Crushed
oyster shells can be purchased at any farm supply store, as they are also used as a suppliment for chickens to
strengthen the shells of the eggs they produce.
Write me at:
Overfeeding is number four on our top ten list of ways to kill your fish.  In the heat of the summer, when water
temperatures are at their peak, you can pretty much feed your fish as often as they'll eat.  My fish will eat every half
hour if I'm there to feed them (the little beggers).  Overfeeding is when you throw too much food in the pond and it
remains uneaten and begins to rot.  Only feed your fish as much as they will consume in 5 minutes.  The only way
you will KNOW how much food they consume in 5 minutes is to watch them eat.  If they finish what you give them
and are still hungry, you can feed them some more, but try to fight the urge to throw a mass of food in so they can
dine on it for an extended period of time.  Fish food goes bad very quickly, especially when it's in warm,
bacteria-laden pond water.  Having a lot of rotting food in your system will produce all sorts of nasties that you don't
want your fish to be around, much less consume, so don't do it.  One of the 'nasties' which grows on rotting food is
Saprolegnia (
Sap-row-leg-nee-ah) or SAP for short.  This slimy, whitish, cotton-like coating can also infect your fish if
they are under stress or on the unhealthy side to begin with.  It's a buggar to treat, as the only thing I have found to
kill it is Potassium Permanganate (or PP), which is HIGHLY toxic to fish if used incorrectly.  Watch your fish eat and
only feed them as much as they'll actually consume in the time you are watching them.  Smaller, frequent feedings
are MUCH better than one giant feeding.  If you still see food floating about in your pond after 5 minutes, or filling
up your skimmer basket, remove it immediately.
Over medicating is yet another good way to kill your fish.  People often over estimate the volume of water in their
pond system, or are a bit lax about reading the directions on the medication label.  If you ever do have to treat your
entire system with a medication, it's important to know the exact volume of your pond. You can find this out in a
couple of ways.  First, when you're filling your pond, you can use the water meter and write down where it is when
you start and where it is when you finish.  Don't forget that your filter box, plumbing, and even your waterfall also
adds to your overall water volume, so when you fill your pond up using the water meter as the gauge, be sure to
have everything up and running before you take a final reading.  The other way to accurately determine your total
water volume is with a salt test.  On
Roark's Experimental Puddle web site, you will find directions on how to do a
salt test to determine total pond volume.  Once you know your total pond volume, write it down or memorize it like
you would your phone number.  It's important information you'll need to know, and when you need to know it, you'll
need to know it in a hurry!
Audio sounds provided by
38391- volivieri water flows over rock.wav
72722 - Manuel Calurano - Conversation
between a nightingale and a frog.mp3
Adding sick fish to your system qualifies for our top ten.  Any time you are adding new fish to your system, you are
potentially introducing something that can kill your existing fish.  If the supplier you are buying from doesn't practise
good quarantine procedures, it's up to you to do so.  The most common disease introduced by new fish is Ich, or
white spot, and fortunately it is easy to treat with salt, however, there are a couple of "newer" virus' that can wipe
out your pond and they are NOT treatable.  Specifically, they are KHV (Koi Herpes Virus), and SVC (Spring Viremia of

For more information on
For more information on

I've said it before and I'll say it again.  Pick only healthy fish from a healthy tank and know your supplier.  
Quarantining your new fish is also of the utmost importance, but few hobbiests have the facilities to do this.  If it is
at ALL POSSIBLE to set up a quarantine tank, it will be worth your effort if you plan on purchasing really nice fish
that you want to keep for a long time.
Using a hammer is a good way to kill your fish.  (Oh, I know what you're saying. "A hammer.  Really?  Hmmmmm.  
Go figure. . . . . .")  Yes, really.  All of us are aware that it's important to keep a hole in the ice over the winter for
the exchange of gasses that build up in the water.  There are several ways to do this, the most common being with
an aerator, pond heater, or small pump to agitate the surface of the water and keep it ice-free.  Unfortunately,
another common (though misguided) way to keep a hole in the ice is to bash it with a hammer.  I've heard many
times how people have walked out onto their frozen pond and bashed a hole in the ice with a hammer, not knowing
that this is an excellent way to kill your fish.  The shock waves created by hammering the ice are amplified under
water.  It's like fishing with a stick of dynamite.  Of course, you won't KNOW that you've killed all your fish by giving
them a concussion until spring, when they all float to the top.  If you are concerned about not having a hole in the
ice, a better method is to use a garden hose.  If you can't hook the hose up to an outside spigot, hook it up to a
faucet inside the house and run the hose out to the pond.  Even the cold water from an outside spigot is warmer
than the ice on your pond, and combined with the water pressure from the hose, you will be able to cut a hole in the
ice as large as you want.  You can then drop in your aerator, pond heater, small pump or whatever.
Copper Sulfate is often used in large farm ponds or golf course ponds to control algae.  Copper Sulfate is toxic to koi,
however, and using it in your pond is a recipe for disaster.  I don't ever recommend using a chemical algaecide in
garden ponds, and all the products I carry are organically based, so there is very little chance for an overdose.  
Anything that says "algaecide" on the lable must be registered with the Federal Government because of it's toxic
nature.  Copper Sulfate is one of these.  Don't use it.  Be patient and use something that will reduce your algae
problem to a managable amount over time.  Your pond doesn't need to be completely algae-free, as some algae
growth is beneficial to your fish.  Nibbling on algae will give your fish something to do, and they'll thank you for it, if
you haven't killed them with Copper Sulfate.
Decomposing leaves and other organic matter is bad for your pond, but some leaves are worse than others.  Not only
do leaves release tannins into the water, which reduces the dissolved oxygen levels in your pond, but some leaves,
such as oak, are actually toxic when allowed to decay in your pond.  If you have a leaf problem, it's best to net your
pond in the fall, before all the leaves start coming down.  In addition to the leaves that fall directly into the pond, the
wind will blow any stray leaves into the pond and they'll stay there and sink to the bottom unless you take them
out.  People are often surprised in the spring when they start netting leaves out of their pond because there are
usually a LOT more leaves than they thought there would be.  It's better to keep the leaves out in the first place
instead of trying to deal with them after the fact.
Sloping the sides of your pond instead of digging straight sides (up & down).  Most things that will eat your fish
(heron, opossum, raccoons, etc.) are predators that catch their prey by wading into shallow water and waiting for
something to swim by.  Installing your pond with sloped sides gives them front row seating to a buffet style lunch
or dinner.  A heron can clean out a pond of it's contents in an hour.  Even if you don't lose any fish, you'll know
your pond has been visited by a predator if your once friendly, happy-to-see-you fish are now in hiding and won't
even come up to feed.  This is one of the reasons I preach installing straight up-and-down sides in your pond.  
Other fish eating predators, such as snakes and bull frogs will not be deterred by straight up and down sides, and
if you have a problem with one of them, your best course of action is to relocate the culprit.