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Nishikoi Koi Know How: DOC and Improving Discoloured Water

A koi pond's stability is often overlooked as one of the most influential factors in maintaining koi health. We can often be guilty of forever tweaking and adjusting water quality in our quest for 'perfect' water quality. With respect to water parameters such as pH and hardness, opinions vary as to what is meant by 'perfect'. Providing koi with a stable chemistry within the acceptable limits is much preferred to continual alterations to water quality in an attempt to hit the jackpot.

Each pond is different and when managed correctly will settle as it matures, developing its own individual characteristics. Factors such as the water source, stocking rates, construction materials and food offered all work in a dynamic fashion to create a unique yet acceptable water quality.

By using 'off the shelf' test kits to verify that the more standard parameters such as ammonia, nitrite, nitrate pH and hardness are acceptable, we can often be unaware of the many 'unmeasured' parameters that may change almost by stealth and without us noticing. It is similar, to say, the experience of having your windows cleaned. Looking through them every day, they may not strike you as being dirty, that is, until they have been cleaned and only then do you realise that they had actually deteriorated significantly over the preceding weeks.

One particular aspect of water quality that can deteriorate steadily in this way (especially to one who sees the water every day) is water discolouration. We are relying on our eyesight rather than the definitive reading given by a test kit and due to its unquantifiable characteristics, can be difficult to analyse. The consequences of discoloured pond water go a lot deeper than simply the aesthetic implications and just as we install a filter system to breakdown the measurable pollutants, we are now in a position to purchase off-the-shelf hardware to solve the problem of discolouration which may underlie a gradual deterioration in the health of your koi.

What causes pond water to discolour?

The culprit for making pond water resemble very weak tea is given an all-embracing term of dissolved organic carbon. (DOC). That is, organic compounds that have some how found their way into the pond, becoming 'dissolved' in the water. Often loosely referred to as protein, the agents that discolour pond water are actually more varied and will include sugars, organic acids, pheromones, phenols and persistent hydrocarbons. These compounds discolour the water usually giving it a yellowish tinge, and will accumulate over time, creating both an unsightly phenomenon and a degree of instability to the water quality. Being organic, many of these compounds attract the attentions of heterotrophic bacteria, which in turn utilise oxygen accordingly. The greater the organic load, the greater the bacterial activity and the more likely it is for a pond to risk facing an oxygen debt.

There are however, dissolved organic compounds that resist breakdown by even heterotrophic bacteria and it is these that largely accumulate in a pond to cause the unsightly discolouration, changing the snow-white skin of your kohaku into an off-white yellow. Levels of DOC will tend to accumulate over a period of time in a similar way to nitrates, with a regular partial water change the traditional remedy, diluting the problem away.

There is, however, a relatively new piece of hardware available, that in the same way as UVcs were introduced 15 years ago to later become a mainstream piece of pond equipment, these too are likely to improve the stability and clarity of our ponds.

Just as UVcs were adapted from industrial applications, the pond protein skimmer employs hardware that has been adapted from the marine branch of the fishkeeping hobby.

Protein skimmers (or foam fractionators) have been used as standard kit in marine aquaria as an aid to filtration and a method of maintaining incredibly stable water quality. As this is also the aim of koi keepers, it seemed reasonable to adapt one for use in freshwater. Protein skimmers perform less efficiently in freshwater as it is less dense than marine water and thus cannot create the same efficient fine mist of tiny bubbles. Nevertheless, its performance in freshwater ponds can be quite staggering with respect to the quantity of DOC that is removed from the pond and the resultant clarity of the pond water.

Protein skimming works by a process called adsorption (not to be confused with absorption) which is the attraction of DOC onto a suitable surface. The process takes advantage of the physical nature of DOC molecules, and something that is all too evident on a foaming pond. DOC molecules cause a foam to form as the molecules which collect at the pond surface cause the pond water to form very stable bubbles. These bubbles remain and form into a foam.

Imagine each DOC molecule to be shaped like a matchstick that behaves with a dual personality. The head likes to be immersed in water (hydrophilic) and will always be wet while the tail end hates water (hydrophobic) and is repelled away from water.

As soon as a bubble forms, these bipolar molecules are attracted to the surface between air and water and accumulate around the surface of the bubble, with the heads pointing outward and the tails pointing inward. This gives the bubble some stability and will resist bursting for some time. Those of us who periodically see a foam on the surface of our ponds are actually observing this phenomenon which is evidence of a high DOC level in the water.

Foam fractionation capitalises on the dual personality of the dissolved organic molecules and involves creating a fine mass of bubbles, encouraging the DOC molecules to create a stable foam. The foam then naturally rises above the water surface, collecting in a chamber which requires either manual emptying or is fitted with a drain to waste.

When a foam fractionator is first installed, phenomenal quantities of foam (and the final brown liquid) are first formed as the DOC molecules are attracted en masse to the air/water interface. Over time, as the DOC concentration drops, so does the rate at which the foam is formed and liquid 'protein' removed. When run continuously, in similar fashion to a UVc, (as a bleed off the main pump or benefiting from its own dedicated pump) once it has cleared the residual problem, it should keep on top of any subsequent DOC accumulation.

Other Benefits of Foam Fractionation.

Besides removing discolouration from the pond water, a protein skimmer helps to maintain the stability of water quality. Once you see what it can remove from your pond water, you may be troubled by your conscience as to what you have been allowing your koi to swim in for the last few years.

Furthermore, the removal of the burden that DOC can place on the oxygen demand created by heterotrophic bacteria will reap benefits of improved oxygenation of the pond and better biofilter performance all round.

Foam fractionation provides us with the ability to provide koi with appreciably better water quality. As DOC is not a standard parameter that can be easily measured, we can be led into assuming that it doesn't exist. Yet seeing what can be removed and achieved when using a foam fractionator should be incentive enough for you to consider the benefits of installing one.

ionator should be incentive enough for you to consider the benefits of installing one.

 

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