This will be one of the few postings I will put up regarding KOI care. This was previously on my geocities website about KOI but unfortunately the said website was taken down last year
Common myths :
* Clear water is a good sign that water quality is good without any contamination
* Constant change of water to "refresh" environment is good for the fish
* One need to invest in sophiscated filtration systems to ensure clear water
To counter above myths one need to understand several important characteristics of water, namely:
pH ( amount of hydrogen ions ) :
This is a measure of level of acidity or alkalinity. Its value ranges from 0 (very acidic) to 14 (very alkaline). Value 7 is neutral. For koi, the ideal value is between 7 to 8. pH changes by a unit represents a ten-fold change in the hydrogen ion content, eg a pH value of 9 is 10 times more alkaline than pH 8. Any tendency of the water being alkaline can usually be offset by rainwater ( which is acidic). Excessive alkalinity could be due to leaching of any rocks with high calcium content in pond, excessive algae bloom. Excessive acidity could be due to overstocking, and leaching due to rotting matter especially plants. Regular partial water changes will help to regulate the pH. You can purchase such pH testing kits in most aquarium shops. Buy a simple kit (eg litmus paper) , don't waste your money on sophiscated meters. pH value fluctuation is normal. I'd not recommend even purchase of chemicals to maintain the pH unless you have a drastic pH problem.
Koi can survive a large temperature range from 4 to 30°C. If your place has winter, it is wise to invest in a heater to maintain filter operations as bacteria growth is crucial to water purity; additional benefit fishes will me more active.
Hardness of water :
This is a measure of level of dissolved substances ( both organic and inorganic ). A simple test to determine level of hardness: Hard water creates little lather with soap, conversely soft water produces more lather with soap. Generally alkaline water will be hard and acidic water soft. A "hard" environment reduces the load on the osmoregulatory ( an internal balance of water and salt level) system of the koi. Koi, being freshwater fish absorb a lot of water into its body. Their salt levels is also higher than the water outside. Through a process called osmosis, pondwater passes through the skin into the body. The Koi removes the excess water through urine. Addition of salt (concentration 0.3%) to the water helps to reduce to load on the fish's kidneys to expel the excess water.
Oxygen content and water temperature :
Koi require at least 6mg/litre of oxygen in the water. If you are unable to measure this, a simple way is to ensure effective aeration through a waterfall or fountain . If you can afford to run your pump for 24 hours this is the best solution. This however is also affected by the population density in your pond. I'd suggest at least a 12-18 hour aeration staggered out throughout the day if you're overly concerned about your electric bill. There're arguments that it's equally important to run the aeration at night as oxygen level is reduced with no sunlight and any algae/plants in the water will still use up oxygen. I feel it's more important to ensure aeration is on when the temperature is higher especially in the afternoons ( as warm water can hold less oxygen and fish's activity higher using up more oxygen ). Temperature effects is more crucial in shallow ponds as water heat up faster. Accumulated uneaten food will reduce oxygen, so don't overfeed. A wise rule of thumb during feeding: amount given in proportion to amount fish can take in 5 minutes.
Carbon Dioxide :
In the day, plants absorb carbon dioxide released by the fishes and oxygen is released as a by-product. At night (with no sunlight) this process is reversed, plants absorb oxygen and release carbon dioxide.If the pond is overstock, this could lead to a drastic drop in the level of oxygen. The excess carbon dioxide can be removed from the water surface by aeration.
Nitrites and Nitrates :
Waste products released by the koi undergoes a process of decompostion by bacteria to ammonia which is further oxidise to nitrites and nitrates. Ammonia is converted to nitrites by Nitrosomonas bacteria , the nitrites produced is further converted to nitrates by Nitrobacter bacteria.Nitrates are absorbed by plants as food completing the Nitrogen cycle. These 2 bacteria require a good supply of oxygen to survive, failing which other bacteria types will takeover and reconvert the nitrates back to nitrites and ammonia. A high level of both ammonia (above 0.2 mg/litre) and nitrites (above 0.15 mg/litre) is harmful and lethal. The level of ammonia nad nitrites is related to pH value. Neutral to acidic water will contain little ammonia. Overfeeding and overstocking are usual causes to high ammonia and nitrites levels. If these levels are high you'll need to make partial water changes (up to 20%) to "dilute" the level. . Simple test kits can be purchased to measure this levels.
Water from the mains is commonly treated with chlorine to kill a wide range of larvae, micro-organisms, bacteria, viruses etc. A simple way to reduce the chlorine ( besides buying anti-chlorine chemicals) is to "evaporate off" the chlorine by either spraying or splashing it into the pond from a height of 5-6 feet to maximise air/water mixing. If you're filling up new it'd be wise to let the water be aerated for a few days before adding any koi to it. High levels of chlorine will make the koi lethargic and eventually sick.
GREEN WATER??? - This is the most annoying and exasperating problem faced by new pond keepers. In my initial year, I've spend my weekends attending to this problem - cleaning the pond, removal of algae blooms, addition of "anti-algae chemical treatments", changing water etc. This time consuming task was often repeated as the water will turn green within a week. Especially in my country where it is HOT HOT everyday, the situation is even worse. I've even contemplated building a shade above the pond to reduce the sunlight hitting the pond directly! Consultations with the local aquarium was always the same - buy this or buy that; there was no clearcut solution to the problem. I decided to do some reading up; bought a few books and it struck me that the KEY to clear water was basically very simple: PROMOTE BACTERIA GROWTH in the filter and REDUCE NITRATES level in the water.