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Water quality

Water quality - introduction

The biggest killer of koi is undoubtedly the knock-on effect of unsuitable water quality. Remember, clear water is not necessary healthy water.

Koi is no more than a domesticated carp (Cyprinus carpio). Unlike their wild cousins that are much hardier, koi has been subjected to inbreeding to such an extent that the immune system has been compromised. Koi are therefore much more affected by their environment.  

The whole concept of our hobby is not only the ability to keep koi, but the ability to keep the water and pond system healthy. Our systems are based on recycled pond water and during the recycling process; a lot of things happen that has a definite influence on the fish.


Nitrogen Cycle
I think by now, most hobbyists understand the nitrogen cycle. In short, the fish excretes waste products trough its gills and urine. An accumulation of these waste products are toxic to the fish especially ammonia. Ammonia is more toxic to fish the higher the pH gets. Colonies of Nitrosomonas bacteria in the filter system convert the ammonia (NH3) to nitrite (NO2). Nitrite is also toxic to fish but then Nitrobacter bacteria converts nitrite (NO2) into nitrate (NO3). Nitrates are relatively harmless and fish can tolerate reasonably higher levels of it.

Ammonia in Ponds
Ammonium (NH4) is released into the pond water through urine and also through the gills of the fish by means of osmosis. Ammonium can also accumulate from the decay of fish tissues, food and other organic debris derived from protein. If the water has a high alkalinity, one of the Hydrogen ions from the ammonium is stripped off, leaving an ammonia molecule (NH3), which is highly toxic. As pH rises, Ammonia becomes more toxic. For example, when the pH is 7 and the ammonia is 0.25 ppm (particles per million), it is acceptable. With the same reading of Ammonia at a pH of 8, the fish will start to stress and complications may start. However, an ammonia reading of 0.25 ppm at a pH of 9 is deadly to fish. Ammonia can have a number of detrimental effects on pond fish such as reddening of the skin, disrupting the ability to regulate water and salts and it can damage the delicate gill tissue causing swelling which can hinder the absorption of oxygen from the water. The lamellae may also become fused and covered in mucus making the absorption of oxygen more difficult.

Dr. Eric Johnson, in his book Koi Health and Disease states: “If a fishes gills are damaged, it cannot excrete ammonia sufficiently. It gets worse if the ammonia level in the pond or tank is high, the fish cannot excrete the ammonia through the gills against this gradient. So the ammonia stays in the fish and kills it. Do not let ammonia accumulate in the water! Fish suffering in water with high ammonia accumulations will isolate themselves, lie on the bottom, clamp their fins, secrete excess slime, and are much more susceptible to parasitic and bacterial infection. Ammonia has been shown to depress the immune system (via the cortisol stress-response on vitally important immune fighter cells) at chronic low levels, below 0, 25 ppm.”

If the water becomes polluted with ammonia, regular partial water changes needs to be effected to reduce the concentration. You must however determine the cause of the problem. My advice is to change water, reduce feeding and expand your filter system if it is already an established one and the ammonia problem persists. You can also reduce your stocking level in the pond.

Nitrite in Ponds
As the ammonia in the pond begins to reduce, the next problem the koi keeper will face is the secondary break down product, nitrite. It will begin to increase and this is also toxic to fish

Nitrite will irritate the skin and the fish will start to flash, gasp and jump. The symptoms are much the same as with parasites and you should eliminate the possibility of nitrite toxicity before you treat the pond for parasites. Nitrite also has a more serious effect on your fish. As it accumulates, it will bind with the red pigment in the blood, thus preventing the blood cells from absorbing oxygen fro the water. Once this happen, the gill filament will turn brown. This is commonly known as “brown blood disease”. Normally fish that dies from nitrite toxicity, die with their gills widely flared.

Lower the nitrite levels with partial water changes and add salt immediately to 3 kg per 1000 liters to inhibit the further uptake of nitrite into the bloodstream. I do not know of any treatment to reverse the binding that has taken place.

Nitrate in Ponds
Nitrate was once regarded as not especially harmful to freshwater fish but as a potent plant fertilizer that can contribute to the growth of unsightly and unwelcome algae, such as green water or blanket weed. Now, when fish are sick, and you know the pond has been set up for a long time, you can bet Nitrate levels are part of the problem. Nitrates are an under-estimated fish killer. Once dismissed as harmless to koi information now exists to suggest this is not true. Scientists initially evaluating Nitrates as a toxin did not test their subjects long enough. Nitrate accumulations cause dilation of the veins in the fins and other health problems. Nitrates may actually be the most important measurement you make in the established pond because it sets the cadence of the water changes you should do. Never let your nitrate levels exceed 100 ppm or illness and vulnerability to disease will be the result!

Alkalinity and pH in Ponds
The pH of a pond is largely dependent on the pH of the make-up water in the surrounding area and therefore it is very difficult to try to control this parameter artificially. Koi can adapt to pH within the safety range and only very experienced and brave hobbyists should fiddle with it. I have seen many koi deaths because eager owners tried to adjust the pH but did not take all the factors into consideration.

pH is the measure of relative acidity and alkalinity with 7 being neutral. pH below 7 is acidic and above 7 is alkaline. A pH measurement uses a logarithmic scale which means that a change from pH 7 to pH 8 is actually a ten fold increase. This is why a small increase in pH can have quite a dramatic impact on your koi. Koi are happy in water with a pH anywhere between 6.8 and 8.5. 

Alkalinity is the carbonate and bicarbonate concentrations in your pond water. Alkalinity is a measure of the ability of a solution to neutralize acid without changing the pH. It both controls and maintains water pH. Carbonate hardness is measured in degrees (dKH), parts per million of calcium carbonate (ppm CaCo3), or milligrams per litre (mg/L).

Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity.  Alkalinity is related to the amount of dissolved calcium, magnesium, and other compounds in the water and as such, alkalinity tends to be higher in "harder" water.   In an established pond, the ideal Alkalinity measurement should be around 100 ppm. Readings from 50 to 200 are acceptable.

Alkalinity is naturally decreased over time through bacterial action which produces acidic compounds that combine with and reduce the alkalinity components.

Ponds with vinyl liners or of fibre glass construction tend to show a decrease in alkalinity over time and may need supplements to maintain an acceptable level.

Established ponds will normally maintain their equilibrium pH value if sludge and decaying organic material is routinely removed from the pond by backwashing the mechanical filter, and biological converter.  Scheduled water changes (10% per week for a small pond, less for larger ponds) are also helpful.

PH can be very, very dynamic. The pH can change overnight. In particular, the pH is prone to fall, and "crashes" are quick, and fatal. Interestingly, many people say they checked the pH last week, and are surprised to find that the pH can change overnight. In simple terms, the pH is supported in range by the carbonate activity of the water and when the carbonates are exhausted, or overloaded, the pH plummets to 5.5 and kills filter bacteria and fish. In other situations, the pH can glide downward very slowly over months and thus your resident fish can survive a low pH but the new fish you keep buying perish quickly as they enter the water with a very acid pH. 

Check the pH regularly, and also, to get a grip on your 'safety net', measure the water's carbonate activity as Total Alkalinity as well.

Raise alkalinity by adding Calcium Carbonate, concrete blocks, oyster shells, limestone, even egg shells or a pH Buffer.

The ideal water readings are:

  • Ammonia – less than 0, 1 ppm
  • Nitrites – less than 0, 2 ppm
  • Nitrates – less than 50 ppm
  • pH – 7 to 8
  • Oxygen – more than 5 ppm
  • Alkalinity – 50 to 150 ppm
  • Hardness – 70 to 150 ppm
  • Salinity – up to 0, 3%
  • Chlorine – less than 0, 05 ppm
  • The temperature for optimum growth of nitrifying bacteria is between 77-86° F (25-30° C).
  • Growth rate is decreased by 50% at 64° F (18° C).
  • Growth rate is decreased by 75% at 50° F (10° C)
  • No activity will occur at 39° F (4° C)
  • Nitrifying bacteria will die at 32° F (0° C).
  • Nitrifying bacteria will die at 120° F (49° C)

Last Updated on Monday, 08 November 2010 19:52