W, X, Y, Z: Pond Keeping Terms – Water Quality to Zooplankton

Water Quality

A short entry in an encyclopaedia cannot do the topic of water quality justice. Water quality is concerned with providing a stable, quality environment through testing water and responding to any undesirable changes from the norm. It is vital to understand how it can be managed and maintained within acceptable limits and how it impacts on the life and health of a koi pond. Put simply, know water quality, no problems.

Water quality in a koi pond interacts fully with the whole life of a koi pond. It is influenced by biological and chemical processes within a pond and it in turn influences other chemical and biological factors associated with the pond.

Our grasp of what is happening within the confines of a pond is best shown by what our test kits tell us. Water, as the world’s best solvent, takes on the character of what it has been in contact with, which in turn influences other parameters within water and its affect on koi health.

These characteristics or ‘parameters’ of water can loosely be grouped under two headings of chemical and biological, although there is significant crossover between these groups.

1. Chemical.

The chemical parameters used to describe characteristics of water include pH, GH, (general or total hardness), and KH(carbonate hardness). These factors are primarily controlled by other ‘chemicals’ dissolved in the water. For example, GH is a measure of the concentration of specific elements dissolved in water (which in turn can affect pH). A good understanding of such parameters and their interactions with each other will enable a koi keeper to provide a suitably stable and well buffered pH, to be able to correct a poor pH through the addition of specific compounds.

2. Biological.

Biological parameters are more concerned with the life of organisms in the water and their knock-on effects and interactions with the water, good or bad. These include ammonia, nitrite and nitrate as well as the lesser well known compounds such as sulphates and phosphate interactions.

The biological characteristics of water will inform us of how the waste that is produced by fish (and other organisms) is being handled and broken down by bacteria in the biofilter. An ideal water quality will require zero readings for ammonia and nitrite and very low readings for nitrate. We should also be able to respond to unfavourable water quality conditions such as peaks in ammonia or nitrite by intervening practically to remedy such problems.

Of all the queries that are received relating to koi health problems or concerns, the majority can be traced back to a water quality problem. Even though there are a key number of fundamental points to grasp in understanding water quality, it is still the single factor that causes the most problems in koi health.

Whitespot (Ichthyophthirius multifiliis)

Whitespot is widely regarded as the most common disease experienced in fish keeping. It is also probably one of the easiest to diagnose. Whitespot is a microscopic protozoan parasite which attaches to fish skin and gills, often causing fish to flick and scratch. Koi are predisposed to whitespot when they become stressed (especially through rapid and extreme changes in temperature). In such instances, when a koi’s natural defences are reduced, free swimming ‘swarmers’ infect external koi tissues and encyst on their skin, taking on the form of a tell-tale white spot. If left untreated, the whitespot infestation can become so extreme as to threaten the life of a koi. The free swimming stage is vulnerable to treatment and such ‘swarmers’ are easily controlled by adding a proprietary whitespot remedy to the pond. Be sure to complete the course of medication to ensure that all the free swimming stages of the parasite are treated.


Xanthophyll (pronounced (‘zanthofill’) is a yellow colour pigment, often found in natural food sources such as algae. Belonging to the huge group of carotenoid pigments, it can be exhibited in skin in yellow chromatophores or pigment cells in koi skin. Feeding koi a diet containing natural colour enhancers such as xanthophylls can help enhance the yellows in koi and other ornamental fish.


Zeolite is an off-white clay-like mineral that has desirable chemical adsorbing properties. It’s use in the koi world is as an ammonia adsorbing substrate that should be used as a short-term remedy for peaks in ammonia brought about by overstocking, overfeeding or filtration problems. As a means of chemical filtration zeolite should be placed as late in the filtration process as possible. Its porous nature makes it very liable to clogging, and it’s efficiency declines greatly if it is allowed to do so.

Zeolite works by itself being slightly negatively charged, bonding loosely to sodium ions which attach to its surface. In the presence of the ammonium ion (NH4+), ammonium ions become adsorbed to the zeolite in exchange for the sodium ions which are released into the water.

Zeolite has a limited effective lifespan, where its ammonia adsorbing properties decline over time. At such a time, it should be removed to be ‘recharged’, rejuvenating its useful properties so it can be used again. Zeolite can be recharged by placing it in a bath of salt water for 24 hours. The ammonia is released into the water and the Zeolite is ‘recharged’ with the sodium ions; ready for use once again.

Ideally, there should not be a call for Zeolite to be used in a koi pond that is managed wisely. It is only required during an ammonium crisis, which if one occurs, can soon be remedied by stopping feeding and carrying out a partial water change, saving on considerable expense.


A collective term used to describe tiny, almost microscopic ‘animal’ aquatic life. Zooplankton include daphnia, copepods and rotifers (Infusoria) and play a vital role in the rearing of koi fry and fingerlings in clay/mud ponds. Mud ponds are purposefully manured and fertilised to encourage an algae bloom, which provides excellent nutrition for a collection of zooplankton organisms. Fry are stocked into mud ponds when the zooplankton population is at its richest, ensuring that the fry have an unmatched source of nutrition on which to feed, 24 hours a day.

If koi fry are stocked too early into a mud pond, then they will soon exhaust the immature zooplankton population. If they are stocked too late, then those insect larvae that colonise waters to predate on the zooplankton (such as dragonfly and diving beetle larvae) will also feed on the koi fry, decimating fry stocks and that year’s production.

Zoug Jar

Intensive koi farming is quite a technological wonderland, making use of gadgets and equipment many which may be adaptations from other uses. The Zoug jar is no exception. Essentially conical in shape, and usually made of a transparent material, (although this is not critical), a Zoug jar is used to incubate koi eggs.

Reportedly named after a Swiss town, the Zoug jar’s design includes a regulated inlet at the bottom and a lipped or spouted overflow at the top. This allows water to be pumped in at the bottom, flowing out at the top, retaining the relatively dense and developing eggs in a constant stream of aerated water.

The flow through a Zoug jar is critical for the development of eggs. Too slow, and the eggs may be encouraged to cake up and clog, too fast and the excessive turbulent action can cause the fragile embryos to be damaged. The Zoug jar is used in mass production of koi, where the brood fish are stripped of their eggs and sperm, fertilised and then incubated en-masse in jars. The less intensive methods involves the flock spawning of selected broodfish in spawning media, where the eggs will remain attached until they hatch. Hatch rates from Zoug jars are consistently greater than those on media as greater control can be exercised over the conditions in which the eggs hatch. conditions in which the eggs hatch.

Kill blanketweed and string algae.