Testing the waters…literally!

Testing the waters…literally!

Your koi rely on you to ensure that the environment you provide for them is healthy; here’s what you need to keep a check on the water quality.

By Angela Beckx

Is your pond water good or bad for your koi? Good water quality is necessary to keep your fish alive, healthy and happy, so it’s essential to ask yourself this very important question often, instead of only when your koi start looking ill. It’s easy to become complacent about water quality if you haven’t had problems, while those new to koi keeping may wonder why they should test their pond water at all if their koi look well – for both these reasons I discuss water quality fairly regularly.

If the variety and apparent complexity of testing kits has scared you off in the past then I urge you to revisit the subject. The tests that will help you to determine whether your pond water is good or bad can be bought at all koi stores and most pet shops. Look for test kits that are simple and easy-to-use and come with colour charts that you can understand. Many of the shops that sell the kits will also test water for a nominal fee and the results will be accompanied by instructions for correcting any problems that have been identified. You need four test kits; one to determine the pH of the water, one to test levels of ammonia, one for nitrite and one for nitrate.

  1. pH

The pH level is a measure of the acidity of or alkalinity of a substance. The ideal range for koi pond water is between 7.2 and 8.5.

Too acidic?

If you test your pond water and find the pH is below 7.2 then the water is two acidic. To increase the pH level (and thus correct the problem) you can add bicarbonate of soda to the water or place crushed coral in the pond. A low pH can cause fish mortalities as well as rendering the biological filter inefficient because the bacteria cannot function well in acidic water.

Too alkaline?

Alkaline pond water often occurs in new ponds that have a cement finish or have been marble plastered because the lime in the cement leaches into the water. A number of water changes or backwashes will usually correct the pH to an acceptable level. If the fish are swimming and eating with no signs of stress at a high pH level then I would leave the water to settle down on its own. If the pH is very high then adding peat moss to the pond is the safest way to reduce the alkalinity. Only experts should use acid to reduce the pH level and then only if the fish are reacting negatively to the high pH. This method in the hands of the uninitiated can be very dangerous for the fish.

  1. Ammonia

Testing for ammonia tells you how much dissolved organic matter and fish waste the water contains. This test is especially important in newly built ponds, as it indicates when to perform water changes. Unfortunately in the first eight weeks of the life of a new pond the ammonia levels climb very high because the beneficial bacteria in the biological filters take time to multiply and become effective. The most desirable reading for ammonia is zero. When the ammonia readings become too high then reduce or stop feeding the koi for a few days. Also perform a 30 to 50% water change (depending on how high the ammonia levels are) and add a biological booster to the filter to speed up the growth of the good bacteria.


Nitrite is a by-product of the bacterial breakdown of ammonia. While nitrite is slightly less toxic than ammonia, it is still very harmful to fish and you again want to avoid levels above zero. Nitrites are easily transported across the gills of the koi and then absorbed by the blood. This is dangerous because the nitrites react with the haemoglobin and reduce the oxygen-carrying capacity of the blood. High nitrite levels cause koi to become very stressed, which in turn makes them susceptible to bacterial and fungal diseases. If you test your nitrite levels weekly while your pond is settling in then you will be in a position to perform water changes to reduce the nitrite levels before problems arise.


Nitrate levels will continuously increase in your koi pond environment as a result of the nitrification process that occurs in your biological filtration system. Nitrate is less toxic than both ammonia and nitrite, however, it must not exceed 150 to 200 milligrams per litre. I recommend setting up a routine of doing regular small water changes so that the level of nitrates never builds up. A strategy of leaving the water for longer and then doing a substantial water change means that algae is likely to proliferate because it feeds off nitrate, so avoid this.

Once you get into a routine of testing your pond water regularly and of correcting any problems you encounter then you can be more confident that you are providing an environment where your koi can flourish. {

Article written by Angela Beckx of Koi @ Jungle. Contact Angela on 031 209 8781 or visit: www.rs02-pta.za-dns.com/~koikzn. Koi @ Jungle also stocks swimming pool products and equipment.

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