Water Quality Problems that Affect Koi and Goldfish
in the Backyard Ornamental Pond

Gosh it makes me ill when I hear so-called "experts" say that a backyard ornamental koi pond or water garden is a "natural" body of water.  It is far from it!  It is an artificial body of water that man manufactures.  It is lined with either rubber or a type of sealed concrete - not dirt bottom where toxins can be absorbed away.  We circulate the same water over and over and over again and it is not fed continuously with fresh water.  We pack so many koi and goldfish in such a small amount of water that it would make Mother Nature gasp with astonishment!  She probably does shake her head at us thinking how stupid we are...

What I'm trying to drive home is that there is nothing natural about a pond that we build except for the natural reactions that take place when you place far too many fish into a captive body of water.  It will not naturally support fish life.  Without circulating the water you have a stagnant swamp.  Without creating a manmade biological filter you have a death trap.  Without pulling the muck off the bottom of the pond you have a sewer.  You want a sewer in your backyard?  Think about how the fish feel...

Goldfish and koi (and other freshwater fish you might stick into the pond) must have healthy water to survive and to stay healthy themselves.  Water quality to a fish equates to air quality for us.  Our air is our environment and when something is wrong with it we get sick and/or die.  We must maintain their home or they will become casualties. 

The Nitrifying Cycle

The nitrifying cycle is the core to a healthy pond ecosystem.  It must be active and strong otherwise the fish end up literally swimming in their own waste.  The simplified version of the nitrifying cycle is this:  Fish eat and give off waste which turns to ammonia which is deadly to the fish.  The aerobic, nitrifying bacteria called nitrosomonas turns ammonia into nitrites (which are also deadly).  The aerobic, nitrifying bacteria called nitrobacter turns nitrites into nitrates which is fertilizer.  The fertilizer then feeds the plants and the fish eat the plants - and so the cycle keeps going.

Whenever there is a missing link the cycle breaks down and the water becomes toxic.  If you don't have adequate nitrifying bacteria you have nothing to change waste into fertilizer. 

Mother Nature cannot possibly supply enough nitrifying bacteria for our overcrowded backyard koi ponds and water gardens without help from us.  Just like you would do for an aquarium you must do for a pond that has fish - you must install a biological filter which will house enough nitrifying bacteria to maintain your fish population.  You can never get enough biological filtration!   For keeping a healthy and clean pond we recommend ProBead or SuperPro Filters.  These low-maintenance filters make it easy to keep the pond clean while providing great biological filtration.

The Most Vital Water Parameters

The water parameters that affect the health of the fish the most are ammonia, nitrites and pH.  The others such as metals, salt, and nitrates affect the fish in lesser degrees but still affect the overall health of the koi and goldfish.  If ammonia and nitrites are present in the pond the fish could easily die.  If the pH suddenly drops it could kill every fish in the pond.  It is extremely important that you keep test kits available in case you have an emergency.  Any time a fish dies or becomes ill the very first thing you do is test the water's ammonia, nitrites and pH.  If you have a reading of ammonia or nitrites or if your pH has crashed you can then learn more about how to treat and prevent these water quality problems by clicking on the In-Depth Information about each parameter located to the right.

Symptoms of Poor Water Quality

Before koi and goldfish begin kicking the bucket often they will display certain symptoms that indicate there is something wrong.  They may hang out by the water return or float just at the water's surface, gasping for air.  They may jump or swim erratically.  Their skin might peel or their fins will look ragged.  They may develop sores (ulcers) and eventually die.  The different water quality issues affect the fish in different ways.  All problems cause stress which leads to poor overall health and lessen the ability of the koi or goldfish to fend off disease. 

The very first thing we must do is to test the water.  We prefer drop test methods because they tend to be more accurate than the strips.  New test kits should be purchased each year - and I'm not saying that to get you to buy more product.  The tests go bad and give false readings.

The breakdown of the nitrifying cycle is not the only thing that can go wrong with the water and cause fish health problems in our koi ponds and water gardens.  It could be low on dissolved oxygen, a toxic substance could be washed into the pond during a heavy rain, or there could be an extraordinary amount of accumulated anaerobic (bad) bacteria and/or heavy metals present.  We could have forgotten to add de-chlorinator when refilling the pond.  The pH could crash or there could be a oil slick.   

First Aid Steps:

• Perform ammonia, nitrite and pH tests.
• Do a major water change if tests results show any trace of ammonia or nitrites (or as a precaution if you don't have test kits available or suspect a toxic substance has been spilled into the pond).
• Adjust and stabilize the pH if it is not between 7.0 and 8.0.

Accidents, Overdoses, Spills and Poisons

• Overdosing of Medications or Water Treatments
• Forgetting to Add De-Chlorinator When Refilling the Pond
• Fertilizers and Weed Killers Being Washed Into the Pond
• Submersible Pumps Leaking Oil
• Submersible Pumps or Lighting Leaking Electricity

What is NOT Poor Water Quality (and not a threat to fish health)

• Green Water
• Foam on Water (unless it is from detergents)

Click on the Statement that Fits Your Situation Best (or Click on the Parameter to the Right for Treatment and Prevention Information)

• My pH is higher than 8.0.
• My pH is lower than 7.0.
• My tests are showing that I have ammonia but not nitrites.
• My tests are showing both ammonia and nitrites.
• My tests are showing that I have nitrites but not ammonia.
• All the parameters are in line but the fish are acting like they aren't getting enough oxygen.
• There is an oily film on the surface of the water.
• There is foam on the water.
• Nothing fits.  Take me to the Diagnostic Clinic.

More Information About Water Quality

• See Our List of Articles on Water Quality

InDepth Information
on Water Parameters
and Problems

Aeration

Ammonia

Anaerobic Bacteria

Chlorine

Heavy Metals

Nitrates

Nitrites

Oily Film

Overdoses

pH

Poisons & Spills

Salt

Know Your Gallons!

Heavy Duty Water Meter

© copyright, 2008, 2009 PondDoc.com.  Reproduction or use of any content on this website prohibited without written consent from PondDoc.com.  This advice is given free of charge and serves as information only to help you with determining the cause of fish health problems.  The content given is to be used as guidelines only.  By following the guidelines on our website you are agreeing that we will not be held responsible or liable for any losses.  We cannot diagnose your specific case.  We are simply forwarding the benefit of our extensive experience with koi and goldfish health.