The pollution solution

Water pollution caused by the injudicious choice and use of koi food threats the health of our koi through creating poor living conditions and should be much more of a concern than our endless headaches about yet another “green-pond-day”.

Koi food primarily provides nutrition, but it is also the main source of waste products in our koi ponds causing the water to go green. These waste products comprise undigested food (such as phosphorous excreted via the feces), unutilized food nutrients (such as excess protein excreted through urine and ammonia), and uneaten food – all overloading the water with non-consumed nutrients that can significantly alter the water quality, for example water enrichment and growth of algae (eutriphication).

In short this reduction in water quality include amongst others the following:

• a drop in dissolved oxygen (O2)
• a rise in Carbon dioxide (CO2)
• a rise in Ammonia nitrogen
• a rise in Nitrate-nitrogen
• a rise in Nitrite-nitrogen
• a rise in Phosphate
• a rise in dissolved suspended solids
• a rise in biological oxygen requirement (BOD)

This accumulation of organic components and metabolic wastes lead to suppression in growth of koi because they now have to compete in a water environment that has a low ability to contain oxygen. Suspended solid materials in the water column may also have a direct harmful effect on the delicate gill surfaces of koi, affecting respiratory function and providing potential sites for bacterial infection. Furthermore, the congestion of pollutants is associated with the release of damaging gasses and hydrogen sulfide and methane, which cause a considerable amount of stress and health risks. As the stocking density increases, the potential for water quality problems in the pond will increase similarly.

Managing water quality means managing the factors that have an influence on water quality. These include:

Correct food choice: Probably, the most effective solution to reduced waste production lies in the correct choice of koi food. We so often prefer to give our koi home-made food because we believe it to be much cheaper, more fresh and much more wholesome - even out of distrust in food companies – or believing that home-prepared diets have a psychological benefit for people who need to give what they see as extra care? Whatever the reason for our preference to this approach towards koi nutrition may just as well create more “holistic” unbalances than nutritionally complete koi foods (“catfood only makes their whiskers grow!”). One example is the breakdown products of excess amino acids from unbalanced foods that directly pollute the living environment of the koi through increased excretion of these waste products. Low pollution commercial koi food typically has the following characteristics:

• It contains the right energy: protein level in order to limit nitrogen excretion. Nitrogen is a waste product of the protein metabolism of the fish, and it is also a pollutant.
• The total phosphorous level in the feed is generally lower than in conventional foods, and it contains ingredients with high phosphor digestibility.
• To reduce organic waste from feed the digestibility of foods and ingredients are improved to encourage higher assimilation of nutrients by animals, which will ensure improved feed conversion and less wastage.
• Water stability of food is improved due to better binding of food ingredients into the food pellet. In this way pellet stability is improved and less leaching of nutrients into the water will take place.
• Low-pollution foods make wider use of alternative protein sources and the elimination of ingredients with unknown anti-nutritional factors.

Correct feeding regime: Dealing with the pollution dilemma is not the sole responsibility of the food producers developing low pollution koi foods, but also of the koi enthusiast. Low pollution foods have no value if it is applied injudiciously in any specific pond – it may even cause more damage through reduced water quality. Overfeeding for example is a common cause of water fouling. In the wild, carp is always searching for food. It is natural for them to continue to swarm at the top of the water surface, “begging” for food even after you’ve just fed them. Many people feel sorry for them and will feed them more. Continuous overfeeding leads an unnatural excretion of waste products – in the long term it even leads to fatty liver disease and death. So, don’t think that they are still hungry, they are just acting normal. The following general guidelines can be applied to improve food management in ponds:

• Feed the fish, not the pond. Koi should only be fed as much as they could consume within about five minutes during feeding time and uneaten food should always be removed from the ponds after 30 minutes or so to reduce the possibility nutrient leaching into the water. Rather split the daily food allowance into several smaller servings than one feeding per day, allowing them to consume the utilize the food better.
• Feeding frequency must be adapted to the fish size - smaller fish need to be fed more frequently than bigger ones.
• Adapt particle size to suit the size of the fish - use bigger particles as the fish mature.
• Distribute feed over a larger area to ensure availability to all fish in the pond. It reduces variation in fish size and waste, and prevents bullying.
• Do not feed when fish are under stress – they will not eat properly. Reduce feed allowance when the temperature or oxygen levels are low or the salinity level is high. When koi are being suspected to be under stress, rather change over to a suitable stress-supporting food such as probiotic paste food.

Effective bio-filtration: It is generally accepted by aquarists that in a healthy pond both total ammonia and nitrite concentrations should be kept at zero. Therefore, the impact of excessive nutrient load on the water quality is significantly reduced by an emergency water exchange – diluting the water to “safe” levels. In static ponds, i.e. those with no filtration equipment, water changes may have to be performed several times per week maintain “safe” to reduce the levels of these unwanted elements. An effectively working mature, pond biofilter are colonised by nitrifying bacteria which metabolise ammonia to deleterious nitrite (NO2-) and ultimately to relatively non-toxic (NO3-). Although non-toxic nitrate, may lead to eutriphication of the water by supplying nutrients for algae growth. Since algae and plants will take up nitrate from the water, they can also be considered part of the biological filter. However being photosynthesizing organisms, they directly compete with the koi for available oxygen during cloudy days and evenings. The bacteria of a biofilter thus play an important role in controlling pollution of the tank with nitrogenous metabolites as well as subsequent eutriphication thereof.

Summarizing: the correct food choice and feeding regimen can be effectively combined to increase the efficiency of nutrient utilization - in this way reducing the chances for pollution. Using a well-balanced premium koi food may at end of the day be a much more contentious thought than scrambling together a mixture just for the sake of “variety”. This, in conjunction with good water quality management through effective biofiltration, represents a significant tool in improving health and longevity of your koi.

Lourens de Wet