Water Quality and Pond Cleaning to Maintain a Healty Pond and Keep Your Koi and Fish Colorful as well as Healthy for a Long Life.
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Water Quality

The provision of good water quality is the foundation upon which all good Koi & keeping is based. Water quality is maintained by having an appropriate filtration system, performing regular water changes, paying attention to stocking levels, consistency in the water source in terms of pH, minerals,and lack of chlorine and chloramine, and feeding the proper amounts of appropriate Koi food. The key here is to adapt the fish to the environmental variables (pH, trace minerals, etc.) over time; Koi will adapt to changes in water chemistry gradually, though they prefer a neutral to slightly alkaline pH (7.0 8.5 and moderately hard water (60 to 120 mg/L).

Water Quality in your pond has to be stable and optimal in order to keep Koi. Your objective should not be for the water in your pond to be so clean and clear that it is virtually sterile. Such a water quality is undesirable and will create many pond fish diseases and they will not develop their best colors. Water being clear is primarily for the hobbyist's benefit. We like to see our fish and it helps us determine their health condition.

Because Koi grow quite large, they require adequate filtration. The length of the fish is not as important as the volume (weight) of the Koi when it comes to filtration.

Water Clarity problems can be traced to 3 sources: over-stocking, underfiltering, and over-feeding.

Clear water can contain many harmful elements that you are unable to see, this is why regular water testing is so important.

Resistance to disease can only be built up by Koi who are exposed to it in very mild doses.

Print out our Water Quality Care Record for Help in Keeping Your Pond In Great Condition.

Poor water quality is a leading contributor to health problems.

Suspended fish wastes are a serious concern for water recirculating pond systems. Large amounts of suspended and settlement solids are produced during fish feeding. Fish waste particles can be a major source of poor water quality since they may contain up to 70 percent of the nitrogen load in the system. These wastes not only irritate the fishs gills, but can cause several problems to the biological filter. The particulate waste can clog the biological filter, causing the vitrifying bacteria to die from lack of oxygen. Particulate waste can also promote the growth of bacteria that produces--rather than consumes ammonia.


If your Ammonia levels are too high in your pond it will cause reddness in your fish's fin and may appear to be bleeding, excess mucus production, flashing, pinecone disease, the fish will lose its appetite, become increasingly lethargic, and general poor health.

High ammonia levels are brought on by access of food, urine and rotting fish waste.

Ammonia, NH3, measured in parts per million (ppm), is the first measurement to determine the "health" of the biologic converter. Ammonia should not be detectable in a pond with a "healthy" bio-converter. The ideal and normal measurement of ammonia is zero. When ammonia is dissolved in water, it is partially ionized depending upon the pH and temperature. The ionized ammonia is called ammonium and is not particularly toxic to the fish. As the pH increases and the temperature drops, the ionization and ammonium decreases which increases the toxicity. As a general guideline for a water temperature of 70° F, most Koi would be expected to tolerate an ammonia level of 1 ppm for a day or so if the pH was 7.0, or even as high as 10.0 if the pH was 6.0. At a pH of 8.0, just 0.1 ppm can be dangerous.

Products to help you lower your ammonia level are Ammo-Lock, Microbe-Lift Ammonia Remover and Dry Ammonia Remover.

Check your ammonia levels every week, more frequently if the system has been disturbed or medicated.

For More Ammonia information Click Here

Signs of Stress

  • Loss of Appetite
  • Clamped Fins
  • Lying Listless on Bottom of Pond
  • Scratching or Rubbing themselves on Rocks or other Items
  • Gasping at the Surface is usually caused by a lack of oxygen in your water or your Koi is stressed.

A great product to reduce stress in fish is Debride Pro Health. Debride ProHealth calms fishs, reduces losses, eases stress, minimizes infection and aids healing.

Important pH Tips for Water Quality

A pH measurement will help us determine if our water is a proper place to put the fish. The pH should normally be between 7.0 and 8.5, but it is probably acceptable to be anywhere between 6.0 and 9.0. Although most of the fish could tolerate a pH as low as 5.0, bio-converter bacteria are subject to damage & you should never let your pond reach this level. Long term conditions above 9.0 can cause kidney damage to the Koi.

pH is basically a measure of Hydrogen ions in the water. High acidity or alkalinity can cause direct physical damage to skin, gills and eyes. Prolonged exposure to sub-lethal pH levels can cause stress, increase mucus production and encourage epithelial hyperplasia (thickening of the skin or gill epithelia) which can sometimes cause fatal consequences.

Changes in pH will affect the toxicity of many dissolved compounds. For example, ammonia becomes more toxic as pH increases.

If your test kit indicates pH of 9 or above and your fish have pale gills and show areas of skin erosion with increased mucus production, you should decrease the pH by adding an appropriate amount of pH Down until the pH has lowered to around 7.5.

If your test kit indicates pH below 7.0 and the fish swim erratically and respire rapidly, a sudden pH crash (Acidosis) may have occurred. In this case you should dose the pond with pH Up until the pH has raised to around 7.5.

pH Crash: Acidosis

Water is constantly rushing (leaking) into the fish through their skin and gills. The kidney is responsible for pushing that water out. Water with a low pH is getting into the fish, and this requires that the body mobilize its own natural buffers to sustain the blood pH. Quickly, these buffers are exhausted and the blood stream suffers a low pH called acidosis. Acidosis can be terminal fish.

For More Information on pH and the pH Scale Click Here

Water Temperatures

Fish are ectotherms, which means that they rely upon the heat that they absorb from their environment to drive their metabolic processes. Fish are surrounded by water, and as they breathe, they are constantly drawing water over their gills. This means that any heat generated by their metabolism is lost very quickly to their environment; as a result, the body temperature of a fish tends to be nearly the same as that of the surrounding water.

Increasing water temperature lowers the amount of dissolved oxygen present, which can cause serious problems, especially in heavily stocked ponds.

Increasing water temperature will cause more of any dissolved ammonia to shift into the more toxic non-ionized form. Your water temperature should not exceed 85° F.

When the water temperatures are cooler the fish are producing less waste and the lower temperatures inhibit bacterial activity.

Koi are cold water fish, but they do benefit from being kept in a heated pond with stable temperatures. In unheated ponds temperature fluctuations cause stress, and Koi are highly susceptible to disease over the autumn, winter, spring seasonal change.

A fish immune system has two parts-the cellular part that includes white blood cells and other hunter-killer cells that actively seek out and ingest pathogens or diseased cells, and a chemical part that consists of antibodies, along with other important compounds such as interferon and complement.

The various parts of the immune system function best at the fishes' preferred body temperature. It has been shown that in a well-researched fish, like the carp, its white blood cells have their highest activity and proliferation at around 83° F, falling off at temperatures above and below this point. Antibody production is optimal at 66° to 78° F, while carp that become infected at low temperatures (below 50° F) do not produce antibodies so long as they are kept at these temperatures. Worse still, some carp that are exposed to a minimal bacterial infection at low temperatures will become immunotolerant. This means that their immune systems will fail to recognize that particular disease-causing bacteria and thus do not mount any sort of immune response, even if the water subsequently warms up.


Nitrate is produced by one of the autotrophic bacterial colonies by combining oxygen and nitrite. This occurs both in the bio-converter and to a lesser degree on the walls of the pond. A zero nitrate reading, combined with a non-zero nitrite reading, indicates the nitrite-nitrate bacterial converter action is not established. Test kits are available with dual droplet or pill form with color charts. The recommended test kit range 0 - 200 ppm.

Nitrate is called the silent killer. It is usually not monitored very well by the average Koi keeper. If the levels slowly become high due to lack of water changes it will cause ulcer disease and death.


Nitrite should not be detectable in a pond with a properly functioning bio-converter. Thus the ideal and normal measurement of nitrite is zero. A low nitrite reading combined with a significant ammonia reading indicates the ammonia-nitrite biologic converter action is not established, while a low ammonia reading with a detectable nitrite reading indicates that the nitrite-nitrate bacterial conversion activity is not yet working.

Nitrite is formed when bacteria process the ammonia. The amount of nitrite in the water is then reduced when another group of bacteria convert it to nitrate. High nitrite levels occur when this second group of bacteria is slow to develop in a new filtration system, or when these bacteria have been damaged or overloaded.

Causes of such damage or overloading include:

Source Of Nitrite

Nitrite is produced by autotrophic bacteria combining oxygen and ammonia in the bio-converter and to a lesser degree on the walls of the pond. Just as with ammonia, nitrite readings may increase with a sudden increase in bio-converter load until the bacterial colony grows to accept the added material. This can happen following the addition of a large number of new fish to a pond or during the spring as the water temperature increases. Fish activity can often increase faster following a temperature increase than the bacterial action does. A bio-converter that becomes partially obstructed with waste and/or develops channels through the media may operate at reduced effectiveness that can also cause the nitrite levels increase.

Effects Of Nitrite

Nitrite has been termed the invisible killer. The pond water may look great, but nitrite cannot be seen. It can be deadly, particularly to the smaller fish, in concentrations as low as 0.25 ppm. Nitrite damages the nervous system, liver, spleen, and kidneys of the fish. Even lower concentrations over extended periods can cause long term damage. Short term, high intensity, "spikes" which often occur during a bioconverter startup or restart may go undetected yet cause problems to develop within the fish months later. A common indication of a fish that has endured a severe nitrite spike in the past is that the gill covers may be slightly rolled outward at the edges. They do not close flat against fish's body.

Fish with nitrite poisoning maybe sluggish, flash or in severe cases, die from lack of oxygen. The gills will take on a brownish or grayish color as the nitrite crosses the gill, binds with hemoglobin, inhibits oxygen uptake and turns the blood brownish.

Nitrite Poisoning

Fish that are exposed to even low levels of nitrite for long periods of time suffer damage to their immune system and are prone to secondary diseases, such as ich, fin rot, and bacterial infections. As methemoglobin levels increase damage occurs to the liver, gills and blood cells. If untreated, affected fish eventually die from lack of oxygen, and/or secondary diseases.

Symptoms of nitrite poisoning:

  • Fish gasp for breath at the water surface
  • Fish hang near water outlets
  • Fish is listless
  • Tan or brown gills
  • Rapid gill movement

Check your Nitrite levels every week, more frequently if the system has been disturbed or medicated.

Treatment Of Nitrite

Whenever 0.25 ppm of nitrite or more is detected in a pond:

  • Increase aeration to maximum. For a nitrite level of 1 ppm or greater, add supplemental air, if possible.
  • Stop feeding the fish if detected in an established pond, reduce amount being fed by half if starting up a new bio-converter/pond.
  • Discontinue use of any UV Sterilizers, Ozone Generators, and Foam Fractionators (Protein Skimmers).
  • For a nitrite level less than 1 ppm, conduct a 10% water change out and add 1 pound of salt per hundred gallons of changed water.
  • For a level between 1 and 2 ppm, conduct a 25% water change out and add 2 pounds of pond salt per hundred gallons of changed water.
  • For a level greater than 2 ppm, conduct a 50% water change out and add 3 pounds of pond salt per hundred gallons of changed water.
  • Retest and repeat above in 24 hours.
  • For nitrite levels of 4.0 or greater, consider transferring fish.

Understanding the Nitrogen Cycle

In a pond, fish will release waste into the water. As the waste breaks down, ammonia is produced.

Ammonia can be toxic if it builds up, so to keep ammonia levels from getting dangerous, beneficial bacteria called nitrosomonas will break down ammonia and convert it into nitrite, which is still toxic if it builds up, but less so than ammonia.

After the ammonia is converted to nitrite, another group of beneficial bacteria called nitrobacter will break down and convert nitrites into nitrates, which are far less toxic than nitrites.

This nitrate is then utilized by the plant life in the pond as a source of nourishment, which helps to keep the nitrate level low and can also help with controlling algae.

So, the nitrogen cycle is essentially the amazing way a pond’s ecosystem cleans itself of harmful toxins and creates sustaining nourishment within its environment.

Nitrogen Cycle

All pond owners must understand the nitrogen cycle to keep water clean.

The nitrogen cycle is an important concept because ammonia, nitrite, and to a lesser extent, nitrate, are all toxic to fish and so their removal from the water is essential for the long term maintenance of fish in ponds and aquariums.

  1. Fish produce ammonia through their waste products and through respiration.

  2. Pond plants produce ammonia as leaves and roots wither and decay.

  3. Beneficial bacteria called nitrosomonas convert this ammonia into nitrites.

  4. More good bacteria called nitrobacters convert the nitrites into nitrates

  5. Some of the nitrates serve as fertilizer for pond plants or algae, and some convert into nitrogen gas.

When this continuous cycle works properly, you get clear water and healthy fish.

If a fish eats a plant or it eats another fish that has eaten plant material, then the nitrogen cycle has been completed.

Unfortunately, one must be aware that in the small volumes of aquaria and in many ponds, the nitrogen cycle does not happen. Nitrate is produced, but the next part, the uptake by plants and algae, does not happen to the extent that we are led to expect. This is obviously the case in aquaria where there are no plants. Most hobbyists want to keep fish, not plants, and so plants play second fiddle insofar as biomass is concerned (except in the most heavily planted aquaria). High levels of fish biomass mean high waste levels that can easily exceed the ability of the resident plants to cope. Even where plants are present, their usage of nitrate as fertilizer (as well as other substances, such as ammonia) depends upon the normal, healthy growth of those plants. This, in turn, depends upon other environmental factors, such as correct lighting (intensity, spectrum, and day length), pH, hardness, iron availability, and so on. In most home aquaria, plants do not thrive, they subsist. Also, we buy plants to adorn our tanks and ponds, not to act as a healthy dietary supplement. If the fish do eat them, we tend to either change the fish or swap to plastic plants.

It is only in well-planted ponds and aquaria with low stocking densities will anything close to a true nitrogen cycle have an opportunity to take place. For most of us, we control nitrate levels either by regular water changes or by using nitrate absorbers, various resins placed into the filtration compartments that lock up any nitrate present. These resins need to be changed on a regular basis.

Carbonate Hardness (KH)

KH is the safety net that keeps the pH from swinging drastically. Being aware of the KH levels is important because much of the biochemical activity in the pond results in acid (released into the water). Sufficient KH allows the ponds pH to remain relatively constant. When the KH level drops too low, it can no longer effectively regulate the pH and that parameter may drop into the harmful (acid) range.

Routine tests of your pond water for KH are recommended and a satisfactory test result is a level above 80 ppm. If regular water changes aren’t enough to maintain the KH, you can add cheap, un-odorized baking soda (sodium bicarbonate, note this is not washing soda). KH levels can be safely (and slowly) raised to 200 ppm.

Carbon Dioxide

Every Pound of oxygen consumed by fish in return they exhale 1.38 lbs. of carbon dioxide. Carbon dioxide does cause problems in recirculating systems where there is no aeration. Carbon dioxide must be removed, or it can build up to dangerous levels.

Oxygen is about 20.9% of the air and because it is only slightly soluble in water, it becomes saturated at a level of about 9 ppm at 68° F (20° C). Carbon dioxide is .033% of the air and is saturated in water at about .5ppm (the ratio is higher because it is more soluble than oxygen). The comparative concentration of these two gases in blood is similar to that of water. Therefore, a lot of carbon dioxide in the water means there will also be a lot of carbon dioxide in the blood of the fish.

An excess of 5 ppm carbon dioxide in the water will affect the ability of the fish to breathe. This is why it is so important to include an aeration system when purchasing your pond equipment. Aeration from fountains and waterfalls help oxygenate the water and drive out excess carbon dioxide.

Dissolved Oxygen Concentration

Dissolved Oxygen Concentration (DOC) is the term given to describe the amount of oxygen that is dissolved in pond water. It is measured in terms of how much oxygen (by weight-mg) is dissolved in every liter of water.

Dissolved oxygen is important to all life in a Koi pond and not just fish. They all have a demand on the finite supply of oxygen dissolved in the pond water. The number of oxygen consumers in a pond will determine whether the dissolved oxygen concentrations in the pond are likely to be a problem or not, with a larger density putting a greater strain on the resource.

A gasping response in Koi will not necessarily always be caused by an unhealthy drop in DO but may also be behavior shown by Koi that is not getting sufficient oxygen to its tissues from poor water quality, specifically nitrite toxicity.

If the toxic nitrite is not being broken down and detoxified effectively by a bio filter it will cause a buildup of nitrite within a Koi's blood and tissues. When the nitrite reacts with the oxygen carrying hemoglobin within the blood, it forms a stable non-oxygen carrying form of hemoglobin, which will make your Koi gasp.

Minimum Water Quality Conditions

Parameter Defintion Preferred Level's How to Correct Notes
Alkalinity (total alkalinity, as CaCo3) The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH. Waters with low alkalinity are very susceptible to changes in pH. Waters with high alkalinity are able to resist major shifts in pH. As increasing amounts of acid are added to a water body, the pH of the water decreases, and the buffering capacity of the water is consumed. If natural buffering materials are present, pH will drop slowly to around 6; then a rapid pH drop occurs as the bicarbonate buffering capacity (CO32- and HCO3-) is used up. 100 ppm   Measures the buffering capacity of water which can be thought of as the sensitivity of pH. It is measured as calcium carbonatee equivalents in parts per million (ppm) or milligrams per liter (mg/l). While 100 ppm is considered ideal, readings from 50-200 are acceptable. Anything below 50 warns that a ph Crash is imminent.
Ammonia (unionized) Excreted from fish gills, also product of organic decomposition. 0 Partial water change, Ammonia Remover, or bind with AmmoLock. Long-term – greater filtration. Possible symptom of too many fish or inadequate filtration. If nitrogen cycle is not functioning well, addition of NiteOut can help.
Carbon Dioxide (free total CO2) The primary sources of carbon dioxide in fish ponds are derived from respiration by fish and the microscopic plants and animals that comprise the pond biota. Decomposition of organic matter is also a major source of carbon dioxide in fish ponds. As part of the carbon cycle known as photosynthesis, plants, algae, and cyanobacteria absorb carbon dioxide, light, and water to produce carbohydrate energy for themselves and oxygen as a waste product. 3   Fish are able to rid themselves of carbon dioxide through the gills in response to a difference in carbon dioxide concentration between fish blood and the surrounding water. If environmental carbon dioxide concentrations are high, the fish will have difficulty reducing internal carbon dioxide concentrations, resulting in accumulation in fish blood.
Chlorine/Chloramine Tap water additives 0 Dechlorinator Always use a dechlorinator when adding tap water.
KH Alkalinity - measurement of carbonate and bi-carbonate in the water 50-150 ppm Raise with SapHGuard, lower with partial water change. Proper alkalinity helps maintain stable pH.
GH General Hardness - measurement of Calcium and Magnesium in the water 50-150 ppm   This is not a critical aspect of pond water chemistry. Adjustments to GH are not usually required.
Nitrite Produced by biological breakdown of ammonia 0 Partial water change. Long-term – greater filtration. Possible sign that filtration is not cycling properly. If nitrogen cycle is not functioning well, addition of NiteOut can help.
Nitrate Produced by biological breakdown of nitrite Preferably less than 20 ppm Partial water change. Long-term – more plants. Nitrate is utilized by plant life. Only toxic to fish in high concentrations (over 150ppm).
pH Measure of the hydrogen ion concentration of the water. Values under 7 are considered acidic, values over 7 are considered alkaline. 7.2 - 7.8 for Koi / 6.8 - 7.6 for Goldfish pH Up or pH Down Check pH at same time each day. It will always be lower in the morning. In general it is better to allow fish to adjust to the pH of your water rather than adjusting pH. The key with pH is stability rather than a specific value. Ammonia is more toxic in water with a high pH.
Phosphate A salt of phosphoric acid Less than 0.3 ppm Partial water changes Phosphates are important and needed by both plants and fish. Excess phosphates can lead to an algae bloom.
Salinity Measure of dissolved salt concentration in the water. Depends on Use Water Change if High, Add Pond Salt if low  

Proper Way To Test

Test kits are only as good as the water samples they receive and the interpretative skills of the operator. If you give the worlds best test kit a contaminated sample, you can expect an incorrect answer. Knowing this, you need to be careful about how you obtain your water sample. Listed below is the Right Way:

Start with clean equipment. Any vials, test tubes, droppers or other apparatus needs to be clean and dry before you start. If you can not manage dry, at least settle for clean. Those hard-water spots lurking at the bottom of your glassware can lead to erroneous pH, KH and even nitrate readings.

Use a Sample Bottle. Ideally, you should extract about a quart of water to use for testing. I've found a laboratory "wash bottle" with a pinpoint dispenser tube and a wide threaded lid to be ideal. This arrangement allows me to simply squeeze the bottle to dispense a very controlled amount of water into a test tube. At 3 bucks, a wash bottle should be part of every serious ponders test kit.

Obtain a clean sample. Submerge your test bottle in the inverted position to a depth of about 8 inches. Rotate the bottle into an upright position so the air escapes and water rushes in. Cap the bottle, then remove it from the water.

Maintain a clean sample. Once you have obtained your sample, keep it out of direct sunlight and maintain the temperature at or near the ponds temperature. Adding heat and light can change pH, dissolved O2 levels, and ammonia readings.

Measure carefully. If the test calls for 5ml of sample water, do not "eyeball" it. Measure it. Some tests (like KH and GH) depend on the water sample changing color after adding X drops of titrant. If your sample size is off even a smidgeon, your test results will be completely bogus. Measure, measure, measure!

Work quickly. Once you have got a water sample, do not let it age more than a few minutes (10 minutes max). Old water can give misleading results. If it takes you more than a few minutes to do your tests, refill the sample bottle. Pond water is cheap and plentiful.

Follow Directions. If the test says "mix gently" then make sure you do not cause to much agitation. Likewise, "vigorous agitation" is not a lazy swishing motion. If the directions call for a certain mixing or waiting time, observe it to the letter.

Keep Your Fingers Out. Do not use your finger as a test tube stopper. There are a number of reasons, the least of which is contaminating the sample. Some of the chemicals used in water analysis are dangerous and you do not want this stuff absorbed into your skin. Use a neoprene cork or plastic snap-cap.

Read the results carefully. Most color-gradient tests (ie, pH) rely on comparing the resulting test color to a standard color scale printed on a paper card. Most color tests are designed to be viewed from the side in indirect sunlight while being held about a half-inch away from their color standard. If you attempt to read the results in incandescent or fluorescent light, expect errors. A discussion of color temperature and color rendering physics is outside the scope of this document, but the effects are very real. One last item that isn't well-publicized is color-blindness. Men: Color tests can be very tricky. If you are male, there is a one in four chance that you can not read a red-colored pH test closer than 0.3 pH points!

Resources: Dallas Koi Pond Doc, K.O.I., Ponds Magazine, Pond Trade Magazine

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Dissolved Oxygen (Heat Stress)

Goldfish, Crucian carp (Carassius), and Koi are three species that switch to anaerobic pathways in times of low oxygen. However, prolonged exposure to these conditions can risk an acidosis of their tissues secondary to lactic acid buildup.

Shade can be provided to fish ponds with either a shade cloth or non-pressure treated wood.

Fish exhibiting signs of heat stress will be congregating at the surface of the pond, near the waterfalls, or any other area where oxygen levels might be a little higher, or where there is shade. The thermometer should aid you in making the diagnosis. Warmer water does not carry oxygen as well as cooler water. At different temperatures, the saturation point varies by as much as 50%, more or less.

In addition to the fact that warm water does not carry as much oxygen, it is know that fish demand more oxygen in warmer water. So at the very same time the water carries less, the fish are wanting more!

Water Changes

Topping off the pond due to evaporation (winter or summer) does not constitue a water change.

Water Changes are important in your water quality. If you can appreciate that a pond is your Koi's toilet bowl, then you will understand the need to flush it.

Evaporation is not considered a water change. You need to change out at a minimum 20 percent of your water monthly. The more you feed and the more fish you have, the more you need to change the water out.

Every owner needs to use some kind of a water quality dechlorinator to remove chlorine and chloramines from new water that is added back into the pond. Chlorine is one of the biggest killers.

There are several full function water conditioners on the market that provide dechlorination along with other benefits, which makes water changes very simple and minimizes the need for several different products. Generally these types of water conditioners are only used when making partial or full water changes.

What are Ammonia, Nitrites, pH, KH, GH and DO?

  • Ammonia is a waste product of fish and also comes from the break down of organic waste. It can seriously burn the gills of fish and cause death.
  • Nitrites come from the break down of ammonia by ‘beneficial bacteria’. It can cause severe damage and/or death to your fish.
  • pH is a measure of how acid or basic a substance is. Below 7 is acidic, higher is alkaline.
  • KH is a measure of carbonate (CO32-) and bicarbonate (HCO3) ions dissolved in the water and represent the main buffering or pH stabilizing capacity of pond water. It helps keep the pH from crashing.
  • GH or general hardness, is a measure of the calcium and magnesium ions dissolved in the water.
  • DO is dissolved oxygen. Koi must have sufficient DO in the water quality to be able to breath and the beneficial bacteria in the filter need it to multiply. The larger the koi the higher the total demand for oxygen.

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How Often Should I Test?

Depending on the season, fish loading, the size of your pond, and basic water quality, you may find it necessary to test anywhere from daily to monthly. For a new pond with an uncycled biofilter, you should test pH, ammonia and nitrite daily for the first two weeks followed by every other day (EOD) for the next two weeks. If ammonia becomes problematic or temperatures are high, daily testing of your water quality for the first six to eight weeks is not necessarily extreme.

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