Water Quality is affteced by many factors, several of which are listed below.  Click on any to learn more:








A higher pH is more critical if your pond is showing an elevated ammonia level.  Ammonia becomes more toxic at higher pH values.

A lower pH is usually a sign that your biofilter is about to or has died.  And the fish will soon follow....

Koi prefer a range of 6.8 to 8.6.  They can tolerate slightly higher and lower, but will be more subject to stress.  Daily fluctuations in pH are even a greater stressor.  The nitrifying bacterial colonies in your biofilter prefer a pH greater than 7.4.  You want your pond's pH to be between 7.4 and 8.6.  For the most accurate pH reading, you should test in the morning (the earlier, the better).

In ponds where the pH has "crashed", the pH will often rise tremendously through the course of the day (could be 5.0 at sunrise and 9.0 at sunset).  If you were to test at 10 a.m.  your pH may read 7.6 (which is a good reading) giving the appearance that everything is fine --- when in reality, it's not.  This is why the early morning reading is so important.

If you monitor your KH and control it with baking soda, your pH will stabilize at about 8.4.


Technically, KH is the measurement of the carbonate ion in the water.  These carbonate ions are neutralized by the acids produced by your biofilter when it eats ammonia and nitrite.  These carbonate ions are the key to keeping a healthy pond.  If their level goes below 50 ppm, your biofilter is either struggling to do its job or it's dead.  The ideal level is between 80 and 150 ppm.  Bead filters (especially during their first 6-12 months) function better at a level of 200-250 ppm. 

Some water sources have an ample supply of KH.  Most don't.  Test your water source also to find out the level of KH you're adding to your pond when you do water changes. 

Raising the KH in the pond is relatively easy.  You add sodium bicarbonate (baking soda) dosed at 1/4 cup per 1000 gallons per day, testing daily, until you reach your desired level.  When your KH tests over 100 ppm, your pH fluctuations will be minimal, your biofilter will be working efficiently and your koi should be happy.

Words of warning while increasing the KH:

If you're showing elevated ammonia levels, you MUST use an ammonia binder.

If you're showing elevated nitrite levels, you must add salt to the pond dosed at 0.10% pond volume .


Ammonia basically burns your fish.  Common signs of ammonia poisoning are fish resting on the bottom of the pond with their fins clamped tight to their body and sometimes a patchy white fuzz-like appearance. 

You want a zero level at all times.  If at any time your pond tests above 1 ppm, you should make a 25% water change --- adding a dechlorinator as needed.  This should be done every other day until levels are below 1 ppm.  Higher ammonia levels require greater/more frequent water changes.  Feeding should be withheld or minimized, depending on the level.  It takes 2-3 weeks in a new system for the bacteria in your biofilter to sufficiently convert ammonia into nitrite.

If you're showing an elevated ammonia level in an established pond it's probably due to one of the following reasons:

1 - you have a build-up of crud (fish turds, leaves or other decaying matter) somewhere in the pond

2 - you haven't been monitoring your KH and your pH has crashed, killing your biofilter

3 - you're overfeeding your fish

4 - you're overstocked

5 - your fish have spawned

6 - you're underfiltered


1 - clean the crud out of the pond and maintain it a little better

2 - bring your KH up with baking soda

3 - feed them less

4 - get rid of some fish or build a bigger pond

5 - add an ammonia binder to detoxify the caustic effects and/or perform a partial water change

6 - get a more efficient filter


Nitrate is not as directly toxic as ammonia and nitrite.  Higher levels are an added stressor and believed to stunt the growth of koi.  Symptoms include overall lethargy, koi that never seem to grow and koi with stressed immune systems opening them up to a wide range of bacterial infections.

Once you start showing nitrates in a new system, you know your biofilter is functioning. To what degree, depends on your other parameters.  You may still be showing ammonia or nitrite, but the cycle has begun (or completed --- depending on how you look at it).  Plants and algae use nitrate as a food source.  Most ponds will have a nice coat of algae on the walls and bottom.  This usually keeps most ponds in the safe zone.  10% water changes every 1-2 weeks will further reduce nitrate levels --- it's good for overall pond health also.  If readings go above 40 ppm, a greater water change is recommended. 

Some of the more common reasons for an elevated nitrate level are :

1 - infrequent water changes

2 - overstocked


1 - more frequent water changes

2 - get rid of some fish or build a larger pond


Nitrite suffocates your fish.  The nitrite molecule binds with fish's hemoglobin making it tough to carry oxygen through the fish's body.  Common signs of nitrite poisoning are the fish hanging out by a waterfall (or other oxygen-rich area in the pond), gasping at the surface and/or red streaks in the fins.

You want a zero level at all times.  Unfortunately, nitrite is not as easily reduced as ammonia is through a water change.  Initially, the level will drop --- but within a few hours, it will have bounced back to where it was before the water change.  The safest way to weather your fish through a nitrite spike is with the addition of pond salt to the pond.  The chloride ion in the salt bonds with the nitrite molecule relieving the symptoms in the fish.  Salt level should be maintained at 0.10% during any nitrite influence.

Once again, feeding should be ceased or minimized depending on the level.  It usually takes an additional 2-3 weeks for a new biofilter to convert nitrite into nitrate.

Some of the more common reasons for nitrite spikes in established ponds are:

1 - build-up of crud

2 - low KH

3 - low oxygen

4 - overfeeding

5 - cold-water feeding

6 - overstocking

7 - inadequate filtration

8 - the filter was cleaned too well


1 - get rid of the crud

2 - raise the KH with baking soda

3 - increase aeration

4 - cut back on food

5 - nitrite should be monitored very closely coming into and going out of winter --- cease feeding until nitrite reads zero

6 - get rid of some fish or build a bigger pond

7 - get a more efficient filter

8 - never clean the entire filter in one shot --- if chlorinated water
     is used, rinse the filter components in a pail of pond water 
     before putting them back in the filter 


Salt does have its place in ponding.  Salt acts as a nitrite binder, mild antiseptic and will kill some parasites.  Always make sure you use an uniodized salt with NO additives, such as yellow prussiate of soda (YPS).  It's not recommended keeping salt in the pond year round.  

Salt should not be added in increments greater than 0.10% every 12 hours.  Two and one half pounds of salt will raise the salinity of 100 gallons of water by an increment of 0.30 %. One pound of salt will raise the salinity 0.12% in 100 gallons of water. 

 ou can (and should) calculate the gallonage of your pond with the use of salt and a salt test kit.  To use the calculator that performs this task, you have to register (no charge) at this website: www.click2roark.com .  There's a wealth of koi related information here. Roark has a knack for making the complex seem simple.  

When dosed as a nitrite binder, salt should be dosed at a level of 0.10%.

When dosed as a mild antiseptic, salt will help with the healing of minor wounds in warmer water.  Salt should be brought to a level of 0.30% for this purpose.

Salt also kills some common microscopic parasites such as chilodonella, costia and trichodina.  Salt level should be brought up to 0.30% for 2-3 weeks.  There are some salt resistant strains that require higher levels of up to 0.60% or 0.90%.  At this level, your koi would probably be better off if you opted for another treatment.

Some pond plants don't fare well with salt.  It's something you should be aware of when dosing a pond with salt.  The main reason you don't want to maintain salt in the pond year round is because of the possibility of developing salt resistant varieties of parasites. 




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