Low Dissolved Oxygen

How to Recognize, Correct and Prevent Low Dissolved Oxygen in Your Koi or Goldfish Pond

Koi and goldfish need dissolved oxygen in the water or they will not be able to breathe.  When there is not enough aeration in the pond the fish suffer and the environment becomes stagnant.  There should not be any "dead spots" in the pond where water does not circulate.  Fountains, air pumps outfitted with air diffusers (or stones), waterfalls and spitting fountains all add aeration to the water.  A pond void of any aeration is basically a swamp and will breed mosquitoes. 

Do not believe that "oxygenating plants" will add aeration to the pond.  It is actually a double edged sword.  Plants give off oxygen and absorb CO2 during the day but do the exact opposite at night.  Plants will rob the pond of its oxygen at night so a heavily planted water garden needs a lot of aeration. 

Many chemical treatments use up the water's oxygen while they work.  Coagulators, such as AccuClear, algaecides and most medical treatments are notorious for zapping the oxygen.  Turning off the pump during a treatment is almost guaranteed to kill the fish.

Many people set timers on their pumps so that during the night when they are not awake to enjoy the pond the pump will turn off.  This is the worst thing you can do.  The worst times for dissolved oxygen in the pond are early in the morning and when the pond water is warm.  Cold water holds dissolved oxygen much better than warm water so during the hottest part of a summer's day is the wrong time to treat the pond or turn off the pump.   

Items You Might Need:

Doc's De-Chlorinator

Air Pumps & Accessories

Plumbed Deorative
Statuary Spitters

Fountains
(coming soon)

Recognizing Low Dissolved Oxygen

The signs that a pond does not have an adequate amount of dissolved oxygen are:

• The koi and goldfish hang out by the water return, especially in the morning, when the water is extremely hot or during a water treatment.
• The fish gulp at the top of the water, especially in the morning, when the water is extremely hot or during a water treatment.
• Finding all or most of the fish dead in the morning and a pH crash was not the culprit.
• The fish start dying during or right after a chemical water treatment.
• The pump was not operating during the night or during the hottest part of the day.

Correcting the Oxygen Level

Add aeration and improve the circulation of the water.  Waterfalls are not the best method of introducing dissolved oxygen.  The best methods include fountains, spitters, and air pump set ups.  The more area where water breaks the surface the better.

Emergency Procedures

1. Perform a major water change.  Don't forget the de-chlorinator if necessary.
2. Make sure all pumps and air pumps are on.
3. If the pump is not working and an immediate water change is not feasible, add hydrogen peroxide to the water for a temporary fix.  Go back to step 1 and 2 as soon as possible.
4. Do not add any chemical other than de-chlorinator or hydrogen peroxide to the pond during this crisis.

What to Expect Next

There may be some residual effect on the pond with bad bacteria especially if the pond has gone a long time without aeration.  Anaerobic bacteria thrives in low-oxygen environments.  This can cause ulcer disease or other bacterial infections to occur more easily because the koi and goldfish are extremely stressed and vulnerable to disease and water quality problems.  Watch them closely for a couple of weeks for any signs of secondary problems.

Preventing Low Dissolved Oxygen

If your fish are exhibiting signs that they are starved for oxygen add aeration by either installing a fountain, spitter and/or air pump outfitted with an air diffuser. 

More Information About Pond Aeration

• Do You Have Enough Aeration in Your Pond?
• CHEMICAL ALERT -- Read this before you add another chemical to your pond

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