Koi Ponds ... Clear Versus Muddy Fishponds
More Top Pond Keeping Tips: Click image right for UK pond products. Use garden pond bottom waste on the compost heap. This organic matter is full of mainly anaerobic bacteria which will catalyse the composting process. Backflushings from the pond filter can be sprayed onto the lawn or garden as a source of nitrogen fertiliser. Ideally the bottom of a fish pond should be kept clear of debris since anaerobic bacteria find their way into this oxygen deprived sludge and create potential infection problems and also reduce oxygen dissolved in the water.
Should koi and goldfish ponds be clear or muddy?
Anyone who is planning to construct or install a koi or goldfish pond in their garden will need to decide on the building method or material they are going to use for the pond. There are a host of options ranging from a carefully constructed concrete shell that is sealed with fibreglass or bitumen, to a mud pond created using the traditional clay puddling technique that was once so popular in Britain.
A filtered concrete shell and an unfiltered clay pond are at either ends of the selection scale when it comes to water clarity. The water in a concrete shell can be filtered and keep spotlessly clear, while it is virtually impossible to guarantee clearness in a clay or mud pool – even if it is filtered. But that doesn't necessarily mean that the former will be any healthier than a pond made with clay. In fact if the quality of the water you fill your concrete pond with isn't proven, you may be subjecting your fish to an environment that is substantially unhealthy!
The pros and cons of muddy versus clear water
The primary argument in favour of a crystal clear koi pond is that you can see the fish swimming around. They are such beautiful creatures it seems a great pity to lose the pleasures of watching them simply because you have provided them with a murky environment. But with water clarity come all the challenges of maintaining water quality.
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A potential con is that the naked eye can't see viruses and bacteria that lurk in the water. This is why our local authorities bombard the water they supply us with, with chemicals. These include chlorine, which is not considered to be "good for" koi.
Most people will agree that when it comes to fish, amphibians, and animals, the best living environment for them is whatever is natural for them. Sparkling, clear water certainly isn't "natural" for fresh water fish, including koi and goldfish. While river water (their natural habitat) isn't necessarily muddy and dirty, it contains pretty well everything the fish need to survive. In fact any well balanced body of water will give them what they need, from a place to spawn to the insects, algae and all the other plants and organisms they find to eat in the wild. In a pond with filtered water, it is you who will become responsible for feeding your koi or goldfish. This means you will need to provide exactly the right type and quantity of food required.
If you plan to breed koi, there is absolutely no doubt that you should opt for a clay pond – if only for raising the fry. Sick and wounded koi also do best in muddy ponds, which are closer to nature than any manmade structures.
Which type of pond is easier to build?
If you are limiting your choice to concrete or clay, it's a toss-up. While clay generally takes less effort to work with (concrete work really is HARD work in more senses than one), it needs to be done correctly. Similarly, if you are using concrete as your building material, it is just as important to use a concrete mix that will hold water. Lime makes mortar and plaster easier to work with, but it is toxic and can kill fish, so it essential NOT to use lime in the plaster mix you use to finish a concrete pond. It is also wise to paint the finished surface with a non-toxic rubberized polyurethane coating to ensure it is watertight. Bitumen is black in colour, which will also give it a more natural-looking finish.
Having said that clay is easier to work with than concrete, it takes a brave person indeed to work with natural clay found in the garden. If you do, the clay content will need to be at least 40% to make it watertight. But clay soils are not all the same, and you might find yourself experimenting before you have a structure that will hold water without leaking. A much more reliable method is to use specially formulated sodium clay.
One product that is available in most parts of the Western world is bentonite, which is mixed with the native soil found on site. Alternatively you can use bentonite matting (if it is available in your area), which is an even simpler solution that negates the need for any mixing at all. Either way, the water reacts with the clay, swelling, and thus creating a reliable seal.
The method used to seal a pond with bentonite clay is remarkably similar to traditional clay puddling. Once the soil and bentonite have been compacted to form the basin that will become your pond, it is filled with water and then left for a few days to allow hydration to take place.
The water in clay ponds
Your unfiltered clay-pond water will never be as clear as in a koi or goldfish pond with filtered water. However you could put a simple biological filter either in the water or on the surface outside the pond. You would, of course, need to use this in conjunction with a suitable pump. However, clay of any sort is quite unlike concrete, or indeed a flexible liner like vinyl, EPDM or butyl rubber, and there will always be a danger that the sand and silt will become churned up either by the fish or the movement of the water.
