Alan’s Book

Chapter 16 Common Terms used in koi keeping circles

New Pond Syndrome

Just for the record the above term refers to a series of events which take place in a new pond.

If we consider a newly filled pond with a filter system at day one, we have the following situation.

Pond -Tap water, which may vary enormously in respect of the range of minerals and chemicals it contains.

Filter system – new material of choice -e.g. K1 media, Jap matting etc.

Fish are introduced and they begin excreting ammonia, both via their gills and in faeces. In response to this food source bacterium, which is usually present in all water supplies, begin to multiply. The initial food source being ammonia encourages those bacteria which utilise ammonia to multiply. The bacteria which use ammonia are a fairly quick growing and convert ammonia into nitrite.

Once a supply of nitrite is available those bacteria which use it as a food source multiply and these in turn convert the nitrite into nitrate.

There is usually a period where the ammonia builds up to high levels as it is being produced more quickly than the bacteria can utilise it. Similarly when nitrite is converted from ammonia there is usually a period when the nitrite builds up to high levels as it also is being produced more rapidly than the bacteria which convert it to nitrate can use it.

The bacteria which convert nitrite are much slower growing than those which convert ammonia; they are also more delicate and as such are more susceptible to water parameters such as temperature, dissolved oxygen and treatments etc.

Due to this it is fairly common for nitrite to remain at detectable levels in the pond for a considerable length of time.

When this occurs the term “New Pond Syndrome” is often used.

In reality many process need to stabilise in a new pond; the reactions as described above for ammonia and nitrite where one process leads to another is a good basis for understanding the actions and reactions which occur.

It is common for new ponds to be „seeded“ with relatively high levels of selected bacteria in order to reduce the time required for the colonies of bacteria to reach levels which can effectively produce good water which has low levels of toxic ammonia and nitrite.

The above information is put in simple terms but I hope it allows newcomers to koi keeping a small insight into what is happening in their ponds.

PH crash and KH

Probably THE main cause of problems in koi ponds is caused by low alkalinity in the supply water to the pond.

Water from our taps is supplied for drinking purposes, not for fish keeping purposes.

Drinking water is collected in reservoirs from rain, and may vary widely in the quantities of minerals it contains, depending upon the terrain surrounding the reservoirs in which it collects.

Water which is most suitable for fish keeping contains dissolved minerals. Of particular importance with respect to fish keeping is the „carbonate hardness“ or „KH“ of the water supply.

It is wise for all fish keepers to learn about the water they have available from their taps so as to ascertain its suitability for the purpose of keeping fish.

The most frequently ignored water parameter is that of „KH“ or the „Carbonate Hardness“ of the water supply.

It is especially important to know the KH of your supply, as this water parameter plays a very important role in systems which rely upon biological filtration to maintain the other parameters which are critical for fish health, such as ammonia and nitrite levels.

The term „PH Crash” refers to a situation where the system PH falls below 6.5 and the filter bacteria cease to function.

Although other factors can cause the failure of filters systems, this is frequently caused by low levels of KH in the pond system, especially in “soft” water areas.


The major processes which are continually occurring in our pond systems are tending to make the pond water acidic. Carbon dioxide, which the fish exhale, and as the end product of nitrification in our filters, tends to reduce the water PH. (Carbon dioxide dissolved in water becomes carbonic acid).

The KH of the water supply indicates the ability of the water to resist changes in ph.

The KH of the pond water is responsible for resisting the pH change; this KH is a usable resource and needs replenishing as the system uses it to maintain pH levels.

Filter bacteria will only operate efficiently under certain water conditions, of which, one of these is a minimum pH of 6.5. Below this level, the filter ceases to function and the ammonia which is continually produced by our fish is no longer processed and it quickly builds up to toxic levels.

Ph crashes can usually be avoided by regular water changes, however some water supplies have very low levels of KH and sufficient water changes may not be practical. Please note that rainwater has zero KH and is not suitable for water changes in koi ponds.

In these circumstances it is wise to add material to the pond system which contains KH. If this can be placed in the last chamber of the filter system, the pond water is continually passed over it, simulating to some degree, rainwater falling upon land which contains rocks which can dissolve and provide KH in the reservoirs in which the rain collects.

These materials include limestone, cockle and oyster shells and lithaqua.

Once a pH crash has happened, ammonia and some nitrite will be detected in the pond water. If the pH is not corrected by water changes or by the addition of materials to provide more buffering (KH) the ammonia will continue to build up within the pond water as fish excrete ammonia continually. Bicarbonate of soda can be used to restore the pH when it has „crashed“.

High levels of ammonia can cause severe damage to the gills and the brain of fish; they also inhibit bacterial activity so even if the correct pH and temperature is restored it is difficult to get the nitrification cycle going again except by large water changes or by adding chemicals which break down the ammonia such that it does not inhibit the nitrogen cycle.

Usually this can be done by trickling water into the pond to dilute the ammonia and restore some of the essential minerals (KH) which act as buffers for the pH.

If the correct conditions of pH and KH are restored quickly it is possible to have the nitrifying bacteria resume their essential work without much delay however temperature will have a significant effect upon this especially if temperatures are lower than ten degrees C and the ammonia remains in the system for a long period of time.

Care should be exercised such that the pH is not raised to a level at which the ammonia becomes toxic. An initial pH to aim for would be 7.0 as ammonia has limited toxicity at this pH throughout the normal temperature range.

It is important that the KH (buffering) of the system is addressed such that further pH crashes can be avoided; regular (weekly) water changes are a good means of avoiding pH crashes and they also form part of an essential routine for helping to ensue the good health of the system.

Pump Fed

This term refers to a system where the pump is positioned in the pond and water is pumped to the filter system and then returned to the pond. The filter system needs to be positioned higher than the pond such that the return water can flow back to the pond by larger bore pipework.

Gravity Fed

This term describes a system where the pond and filter system are arranged at the same level; the pond is connected to the filter system by large bore pipes the water is returned by pump to the pond. This creates a difference in the water levels and encourages the pond water to flow into the filter system via the large bore pipes in an effort to maintain the water level. Large bore pipes are necessary here such that the water flows into the filter system „by gravity“.

The flow rate to and from the filter system will be equal, but the water returned to the filter will travel more slowly through the larger bore pipe and the larger particles of solid waste remain intact, facilitating their removal.

This is the preferred method of water circulation for koi ponds as pump feed systems tend to macerate the solid waste which makes its more difficult to remove.

“Hard” and “Soft” water.

These terms are explained at some length in previous chapters however for completeness soft water contains low amounts of dissolved calcium and magnesium and hard water contains relatively higher quantities of these essential minerals.

A few stories

A koikeeper phoned me and asked if I would check out one of his best koi which had suffered some damage in his pond. I agreed to do so and he duly arrived about an hour later with his koi in a plastic bag.

The koi was on its side and there was no apparent gill movement; the bag was opened and the koi was placed onto a damp towel for examination. The wound on its side was substantial but unlikely to be the cause of the apparent demise of the koi!

“Well” said the owner “I don’t know what’s happened here. I even took the precaution of inflating the carrying bag with Brewery Oxygen to safeguard the koi for the journey”

I queried his “Brewery Oxygen”?

“You know” he said “The oxygen that breweries use for their beer”.

The koi was quickly placed into fresh water with an airstone and it slowly recovered consciousness.

The “Brewery Oxygen” was in fact Carbon Dioxide which had anaesthetised the koi n the carrying bag!


I had a frantic phone call from a person who had a display pond containing koi as part of the décor for his business. He had experienced several problems previously where his fish had been much debilitated having severe whitespot and gill fluke problems. Several koi had succumbed to these infections before he called me in to sort the problem.

“All my koi are jumping about in their pond and there is lots of foam around the waterfall. I fear someone has added soap to my pond. What should I do?”

I immediately travelled to his pond only to find the koi happily spawning!

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