Pond Metabolism – How balanced is your koi or garden goldfish pond?

Every pond is faced with the task of processing products and materials. In so doing it can behave in a similar way to an animal that is shaped by the quality and quantity of food that it eats. By trying to balance the pond’s ability to ‘ingest’ and ‘excrete’ certain materials we can change the characteristics of a pond for the better, improving the long-term health of our koi.

When I was a teenager of between 13 and 16 years of age, as is probably the experience of the majority of teenagers at this stage of development, it seemed I could eat as much of anything I chose and remain the same weight.

My older relatives often remarked and looked on with amazement (and jealousy) as I struggled to put on weight while the opposite was true for them on a diet containing only half the calories of mine. Unfortunately, those days of care-free eating don’t last, and I now know from first hand experience exactly how my older relatives really felt.

So what was happening to me then that is no longer true at my present age, and what has all this got to do with understanding how we can maintain a healthy and balanced pond?

Well the answer that explains the different effects eating can have on your body when you’re 16 and 60 relates to our metabolism. Our pond’s metabolism can also determine both the functioning and health of our pond environment that we provide for our koi.

The term metabolism relates to all of the natural biochemical reactions that occur within a living organism (such as digestion and the manufacture (synthesis) of compounds). When I was a teenager, my metabolic rate was much higher than it is now, and consequently, I was able to handle and utilise far more energy than I can now.

In a similar way, the concept of ‘total pond management’ regards a pond as a single living system, having a metabolism in the same way as a living organism, having to cope with specific inputs and outputs. The pond’s metabolism will govern how it performs and handles its own varying inputs and outputs, which will in turn determine the quality of the pond water and the health of the organisms that it supports, which of course, ultimately includes our koi.

A teenager’s metabolism is regulated by hormones that control growth and hence appetite, whereas a pond’s metabolism is regulated by the ambient temperature and is fine-tuned by the relative rates of inputs and outputs of each organism that has a niche and role to play in creating the pond’s eco-system. Whether we relate metabolism to an artificial clear and filtered koi pond or a more ‘natural’ clay pond, all organisms within each setting will metabolise products specific to their own requirements.

The fundamental difference being that those pond organisms in a natural pond are more likely to be in balance with each other while the recirculating koi pond relies on artificial inputs (food) and outputs (water changes). This kind of system is more likely to experience problems associated with mis-matched metabolic processes of organisms in the pond. In a self-sustaining balanced natural koi pond, the metabolic processes of algae, bacteria, protozoa, invertebrates, insects and vertebrates (including fish), will be more tightly inter-linked, feeding into each other, ultimately producing a more stable environment for koi. Consequently, the metabolism of pond organisms will affect water quality in two ways (which will in turn affect the health and metabolism of our koi).

These are:

1. Gas exchange (i.e. the balance and exchange of oxygen and carbon dioxide)

2. Exchange of dissolved nutrients (i.e. this will determine whether products such as nitrates, phosphates and sulphates accumulate or are in balance with those other organisms whose metabolism utilises them).

1. Pond Metabolism and the oxygen / carbon dioxide balance.

In a natural water body, the production of oxygen via plant photosynthesis and diffusion from the atmosphere sets the benchmark that governs the aerobic life that the pond can sustain. The oxygen consumers (bacteria, invertebrates, fish etc) populate the pond to a level that can be sustained by the oxygen producers (e.g. plants). These organisms also release a corresponding level of carbon dioxide back into the water that completes the cycle, being taken up by aquatic plants as they photosynthesise.

However, in a plant-free koi pond, such an intimate cyclic relationship between plant metabolism and that of oxygen consumers cannot be sustained naturally, leading to the requirement that additional oxygen must be added (in the same way as additional food must also be added) Aeration and water movement in a koi pond meets this need, which also helps to gas-off any excessive accumulation of carbon dioxide which will not be absorbed from the water in a plant-free system.

2. Pond metabolism and water quality.

You will have noticed how a pond’s natural annual cycle through the seasons sees its characteristics change, in a similar way to hormones regulate a human’s metabolic rate. The winter months, (when the cold water temperature dictates the pond’s slow metabolic rate) equates to the slow metabolism of an adult, whereas the hyper-active rapid-cycling metabolism of a summer pond equates to the faster metabolism of an adolescent. If for some reason a winter pond is inundated with excess food energy, it would lead to problems in the same way as if an adult was to over eat.

Because all pond organisms are cold blooded, their rates of metabolism fluctuate at the same rate as each other, depending on the water temperature. Consequently, algae growth and the production of natural live food is negligible in winter, but so is the demand for these food organisms by animals (such as koi) further up the food chain. Conversely, when fish metabolism in summer requires a regular supply of food, the metabolic rates of algae and other food organisms respond in an obliging manner.

Transferring this scenario to an artificial koi pond, water temperature determines the metabolic rates of our koi, and those of our beneficial and crucial filter bacteria. Fortunately, as the koi’s appetite and demand for food increased, (with a knock-on effect of increased excretion of ammonia), so the metabolic rates of bacteria increase (and their ability to divide and populate) meaning that there is no build up of toxic ammonia in the pond. But we can foresee problems happening if we offer our koi too much food. Unlike a natural, balanced pond, in a koi pond there is a real risk of the quantity of artificial food being offered being too great and out of balance with the rest of the ponds metabolism. This is not necessarily a direct problem for our koi (that will eat an unnaturally large meal for the season), but will have negative consequences for the water quality as it is unlikely that the filter bacteria will be in a position to cope with this unnaturally high input of food for the time of year.

This can also shed a different light on heating a koi pond over winter. A natural, balanced pond would start to malfunction if it was heated over winter as the shorter days and reduced sunlight would not be sufficient for algae to grow, thereby not meeting the enhanced food requirements of fish and invertebrates brought about as a result of the heated water. Whereas, in an artificial setting, where the food is added to the system artificially, the pond’s performance is not adversely affected by the fish’s elevated appetite. As an aside, there has been an increase in the number of reports of koi not spawning in a heated pond, but retaining their eggs in a bloated state through to the autumn. This is likely to be as a result of koi receiving mixed and contradictory messages from their environment. I.e. The temperature is informing the eggs to develop and be retained, but there is no corresponding increase in daylength to stimulate spawning.

Blanketweed – A symptom of a pond’s poor metabolism.

Blanketweed is probably the most common problem suffered by artificial koi ponds as a result of imbalanced metabolism in a pond. Very rarely seen in a natural water body that is free from man-made influences, blanketweed is an ever-present curse to most clear and artificially filtered koi ponds. Why?

Blanketweed occurs because the rate at which nutrients such as phosphates and nitrates enter the pond are unnaturally excessive, entering via tapwater and koi food. Excessive quantities of food, relative to the pond’s volume results in an unnaturally high accumulation of nutrients on which blanketweed thrives. This is not to say that blanketweed is not found in a natural lake or pond, but simply that its growth is kept in balance because of the restricted amount of nutrients that cycle through such an ecosystem. In addition, a plethora of organisms graze and feed on blanketweed, preventing it from growing out of hand. If a filtered koi pond was allowed to revert back to a natural stocking density, coupled with the associated turbidity of a clay pond, you would soon find the blanketweed start to disappear.

In contrast, it is very rare for a situation to occur where an excess of animals thrive as such conditions (i.e. an abundance of food) will not exist for very long. The food is soon exhausted and the accumulation of nutrients causes the population to check its own growth. Yet such a situation (e.g. an abundance of food) occurs in every koi pond on a daily basis through the provision of artificial food and it is this that satisfies the metabolic requirements of the stock of koi – often leading to a subsequent imbalance problem (e.g. high nitrates, phosphates and blanketweed).

Trying to achieve the impossible?

In summary, yet again, we have seen how an intricate and well balanced pond ecosystem operates to provide koi with a stable and healthy pond environment. By keeping koi in an artificial pond system, we forego some of the stability for the sake of being able to view our koi in unnaturally high stocking densities. By doing so, we must take action to try and balance the metabolic processes within a pond – something that is practically impossible and unachievable, leading to a number of common side effects such as blanketweed and the risk of water pollution through over feeding. However, whenever possible, we should endeavour to manage our ponds in a way that enables it to support our koi in as healthy and stable an environment as possible.bles it to support our koi in as healthy and stable an environment as possible.

Kill blanketweed and string algae.