pH in koi pond and importance of pH balance


What is pH ? The specification of water pH

The pH or potential hydrogen (concentration of hydronium ions H3O+) is used to measure the acidity or alkalinity of water. In a test, neutral water is at pH 7, on a scale of 0 to 14.

For the majority of freshwater aquatic species (fish, plants and micro-organisms) the optimal pH value for the tank is between 6.8 and 7.5 pH units.
However certain species or situations might call for other ranges: Discus prefer the rather acidic pH 6.2; pH 8.1, somewhat basic, is better for some African Cichlidae; a pH of 8.2 to 8.5 is quite basic, but ideal for a seawater aquarium.

water pH test kit

Some species adjust pH and water hardness range table

Acid pH 6~7.5

Hardness 50mg/L CaCo3

Neutral pH 7.5~8

Hardness 150~300mg/L CaCo3

Alkaline pH 7.5~8

Hardness 300~450mg/L CaCo3

Range pH 6.5~8.5

Hardness 50~350mg/L CaCo3

Pterophyllum scalare,

Botia macracantha,

Symphysodon discus,

Rasbora heteromorpha,

Aphyosemion and Wpiplatys,

Paracheirodon innesi,

Papiliochromis ramirezi, serrasalmus nattereri,


Poecilia hybrid,

Cyprinus carpio, Carassius auratus, peocilia reticulata, melanotaenia and bedtia, Xiphophorus helleri,

Haplochromis, hemichromis, julidochromis, melanochromis,pseudotropheus, tropheus Aequidens pulcher, Corydoras, thorichthys meeki, gouramis/colisa and trichogaster, labeo bicolor, barbus conchonius, betta splendens, barbus tetrazona,





Why ammonia is toxic to fish in pond water?

Ammonia is a nitrogen waste released by aquatic animals into the production pond environment.  It is a primary byproduct of protein metabolism.   Ammonia is excreted directly from the fish gill into the water.  Ammonia concentrations are usually at their highest late in the production season when biomass of the cultured species and the amount of protein fed are greatest.  Ammonia is toxic to aquatic life and toxicity is affected by pond pH. Ammonia-nitrogen (NH3-N) has a more toxic form at high pH and a less toxic form at low pH, un-ionized ammonia (NH3) and ionized ammonia (NH4+), respectively.  In addition, ammonia toxicity increases as temperature rises.


 What is pH means? Defination of pH

The measure of whether water is acidic, basic (alkaline) or neutral is known as pH.  A scale of 1 to 14 is traditionally used, which represents the negative logarithm of the hydrogen ion concentration.  A pH of 7.0 is neutral; above 7.0 is basic and below 7.0 is acidic; close to 7.0 is weak and far from 7.0 is strong.  It is a common perception that the pH of water is neutral and constant at a value of 7.0.

The normal pH of water is 7.0, does it forever be the same?


 Factors that may affect pond water pH:
  1. Photosynthesis and Respiration

Pond CO2 concentrations and pH, are affected by respiration and photosynthesis.  Carbon dioxide is released during respiration and consumed for photosynthesis.  As a result, pond pH varies throughout the day (Fig. 1).


pond water pH and tempeature relationship





The daily interplay of photosynthesis and respiration creates a cyclical change in pond pH.  Pond water becomes most acidic just before the period of darkness ends and most alkaline after several hours of daylight.  The presence of un-ionized ammonia, the toxic form, increases as pH rises and decreases as pH falls which causes ammonia to become more ionized.  The concentration of un-ionized ammonia in production ponds is lowest just before dawn and highest late in the afternoon.

Process analysis:

Early Morning: Absorb CO2 for photosynthetic production of sugar.  As daylight progressively intensifies, the rate of photosynthesis increases and so does the uptake of CO2.  The removal of CO2 reduces the concentration of carbonic acid, and pond pH rises.

Late Afternoon: Late in the production season, high waste nutrient concentrations can promote dense phytoplankton   blooms   which,   in   turn,   can remove all of the CO2 from pond water during photosynthesis.  This can cause the water to become alkaline with pH levels greater than 9.0.  Pond pH is highest late in the afternoon — a few hours before sunset.

After sunset: photosynthesis and CO2 uptake stop. However, respiration continues day and night.  During respiration, plants and animals consume oxygen to free the energy stored in food.  The end product of respiration is CO2, which is released directly into the water.  As photosynthesis is halted by the absence of light, CO2 begins to accumulate and the carbonic acid concentration increases.  The rising concentration of carbonic acid causes the pH to fall. Toward the end of the production season, the biomass and respiration of cultured animals and phytoplankton is high. Nighttime concentrations of CO2, and therefore carbonic acid, can become excessive, lowering pH below 7.0.  As such, pond pH would be lowest an hour or two before sunrise.


Example of water temperature with water pH relationship

This has significant implications for water quality monitoring, especially several weeks prior to harvest when fish biomass is greatest.  For example (Table 1), a producer measures water quality at 0400 hr.  The total NH3-N concentration is 2.7 mg/L, pH is 7.0, and water temperature is 28 ℃.  The farmer then cross-references these values with a standard, pH-temperature table and calculates the concentration   of   “un-ionized”   NH3-N  to  be 0.019 mg/L.  The  producer decides to check water quality again at 1600 hr and finds that total   NH3-N  is  still  2.7  mg/L.  But,  pH   and water temperature have risen to 9.0 and 30 oC.  After checking the reference table, the farmer discovers that the un-ionized NH3-N concentration is now 1.2 mg/L.  An un-ionized NH3-N level of 0.019 mg/L would be considered    acceptable    for   channel   catfish production.  However, the un-ionized NH3-N concentration of 1.2 mg/L recorded at 1600 hr could be lethal to channel catfish within several hours.  Over a 12-hr period, the un-ionized ammonia concentration increased approximately 63-fold.  The temperature change accounts for less than 10% of the increase in toxicity while the rise in pH from 7.0 to 9.0 is responsible for more than 90%.













0400 hr

1600 hr














Table 1.  Amount of total ammonia-nitrogen (Tot/NH3-N) present as un-ionized ammonia-nitrogen (UI/NH3-N), for early morning and late afternoon pH and temperature measurements in a hypothetical production pond.

Measuring pH and Ammonia

When your pond and aquarium is experiencing pH imbalance, there are no visible signs. Since a small change in pH means a drastic change in alkalinity or acidity, it is important to monitor pond and  aquarium pH frequently. Keep a notepad to record your pH readings whenever you test. It will help you recognize patterns and find solutions when something is altering your pH. Before long, you’ll be a pro at using pH conditioners to stabilize pond and aquarium pH.


Plan on regular tests, at least every 2 months. The pH test is a very simple, comparative colorimetric test, very easy to do yourself. pH tester

Four details help you keep koi pond

When processing a pond construction, some subtle details may be ignored. These details are playing an important part in your pond fun.

  1. Avoid unflowing water.  Avoid “dead” It is very important to keep the whole pond water flowing all the way. The pond bottom should be built like a bowl with some curves. At the corners, water could be easily be stuck if the wall is vertical and the bottom is flat. You can not make it as round while you can build the bottom tilting to the central, like a cone.


  1. The depth of water.  How deep should the pond water be? To consider these things: You need to set some overflow outlets to drain out leaves or other waste as well the rains. The function of overflow outlet of the pond is important, one of it is to control the depth and surface water. The minimum depth for koi pond is 80cm from bottom to surface based on the size and area. Sometimes the depth can be deep as 3 meters, most of the pond depth range from 1 meter to 2 meters. Two times of the length of fish would be fine.


  1. Pond wall, pond bottom, and drainage.   The pond wall should be vertical and the bottom should be based a 20 angle to the central. The water flow should flow along the pond wall. Build more than one drainage if possible and one in the deepest bottom of the pond.


  1. Consider pond situation.  Allow some lights in the morning shining on your pond, which will help fish to get a brighter color and also avoid bacteria colonize. Get rid of cold winter wind blowing and take measure to keep it warm, use a heater for example. Plant some trees to make some shelter for fish if possible. Keep fallen leaves or weeds away from clogging the inlet. When there’s too much waste of fish manure and fish food, pipes will get clogged easily. Use a Mountain Tree Skimmer, could be a help in controlling water flow and collect waste as well.