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Design Tips & Tricks

Aside from the physical aspects of actually building your pond, there are some design issues which can help make this a worthwhile project, now, and in the long term.

The first thing to consider is size and shape.  If you're using a preformed pond or water feature then the decision is taken out of your hands, for all other types of construction read on..!    I can't tell you what the perfect shape and size is, I can only list the pro's and con's involved.   In general terms, the bigger, the better, certainly where fish are concerned, but remember that it is essential to match all the various components.  It is silly to build a small 2000L pond and waterfall and then install a 30,000 l/h pump to drive it.  Its equally wrong to build a 8000L pond and install a 2000L filter and UV.   It is generally accepted that fish ponds need the water to be circulated through the filter about once per hour, so for a 5000L pond we would use 4000 - 6000 l/h pump and a 6000L filter box. 

Just a quick word on filters, it is always better to over-filter than under-filter.  Most filters are rated by pond capacity, i.e. "Suitable for ponds up to xxxx litres or gallons", but its worth noting that this usually refers to lightly stocked Goldfish ponds, (makes the filter specification look better).  If you intent to keep Koi you would do well to divide the rated filter capacity by at least 2 or 3.  Some of the better manufacturers such as Oase, advertise much more realistic ratings for their filters and give separate capacities for both Goldfish and Koi.

Today many filters have UV lamps already built-in, and these are correctly rated for the suggested flow rates of the filter.  If you are using a separate external UV then it is important to use a pump with the correct flow rate.  Too small and it will not circulate the pond fast enough,  too big and the water will pass thought the UV so fast that it does not get a full dose of  UV radiation.

So far we have talked about size in terms of cubic capacity, but we could have a wide shallow pond, or a narrow deep pond, both of the same capacity.  Again all I am going to do is list the Pro's and Con's. For good oxygen exchange a big shallow pond with plenty of surface water movement is best, but it is more prone to Blanket Weed and Green Water problems.  The lack of depth may also leave the fish more vulnerable to attack from predators such as Herons or domestic Cats.  A deep pond on the other hand offers better thermal properties during a cold winter and many Koi enthusiasts claim that 1.80M should be considered as an absolute minimum.  Bear in mind though, Water Lilies don't like water deeper than about 50cm - 80cm, (not that you'd keep Water Lilies with Koi, they would just eat them).

Shape is particularly important when using a liner.  Many people can't quite grasp the concept of convex and concave surfaces, especially how they relate to the use of a pond liner.  Without getting into the mathematics of surface mapping lets just look at some examples.

Easiest of all is the shallow square or rectangle which requires one simple fold in each corner. The size of the fold gets bigger with depth, but you still only need one. Next is the square or rectangle with rounded corners.  This requires a number of smaller folds in each corner, and again the size of the folds increases with depth.  If we extend the rounded corners eventually we arrive at a circle or oval and this requires many small folds right around the perimeter, but is still easy enough to do neatly.  Top points for difficulty must go to the kidney shape.  It is difficult, but still doable provided that the kidney shape is not to exaggerated.

When we start to add planting shelves around one or more edges things do become much more complicated and its all to easy to end up with huge folds which are impossible to hide.  As before the simple rectangle is still the easiest, followed by the rounded corners and then the circle. Beware however, even a modest kidney shape soon becomes impossible, the folds around the bottom curves prevent you from covering the planting shelf and still being able to fold up and over the top. Perhaps it is possible in theory, but I don't know anyone who has been able to do it in practice.

Koi and Goldfish in a Garden Pond