Ten Ton Pond

The pond is gravity feed with a bottom drain (there are two basic methods of circulating the water through filters etc and I won't elaborate into them here. If you don't know what I'm talking about, then do a web search for 'koi pump fed or gravity' or something similar. There is a lot of explanatory material out there). I chose a gravity fed system because it seemed to me the most elegant and the overwhelming weight of advice was that it is the best. The main advantage is that water is taken from the very bottom of the pond for treatment and so seems likely not to leave much rubbish behind.

The water is circulated using a pump to a single inlet at the pump end. My first idea was that I would have two returns to the pond, at opposing corners of each of the two long sides. This, I figured, might 'swirl' any debris to the centre. But on reflection, I figured that the simpler the setup, the less there was to go wrong. I think that probably mine is about as simple as the water treatment setup can be. Water comes up through the filter, through the pump and then past the UV treatment unit. Having the UV last is perhaps slightly less than ideal, as dead algae is returned to the pond, but we'll see how it goes. I reckon it'll sink and be filtered out along with the rest of the waste.

As far as filtration is concerned, there is a bewilidering amount of choice. From purpose-built simple and multi-chamber units, through home-built set-ups, biological filters, pressure filters, trickle towers, vortexes and so on.. For the novice (me), this is complicated by the amount of opinion out there! I chose the Nexus Eazy Pod, which is a compact, integrated unit. My decision was influenced mainly through having a small space to put my filtration. The Eazy Pod is small (in filter terms) and seems to be fairly straightforward to maintain - you blow air up through the filter medium, which agitates it and the filtered debris falls to the bottom, where it can easily be flushed away. They also seem to be well regarded, though it has to be said that there are detractors. Lastly, the Eazy Pod (according to the information from Nexus) seems to be the ideal size for my pond.

I didn't think about aeration at the start, which I (slightly) regret. You need aeration because, especially in hot weather, the fish can get short of oxygen in the water and this can kill them. If you have a waterfall or fountain in your pond, you will see that the fish congregate around it when the weather is hot. This is because the oxygen levels near the splashing water are higher. Oxygen is more soluble in cold water than warm, which means that oxygen levels are likely to be less of a problem when the water is cold.

As I said, cleaning for the Eazy Pod filter is carried out through use of an air pump. The pump comes with a length of air hose, a manifold and a couple of air stones. So it's easy to provide aeration. Excellent! So, why do I regret not thinking of it earlier in the build? Well, it's because I now have two transparent air hoses hanging over the otherwise clean edge of my pond. Also, when you turn the air on, the hose becomes lighter than water and so floats up - so I've had to weight it down. I could have avoided this if I'd though in advance and either fitted an aerated bottom drain (that has the air hose running under the pond) or made some other arrangement for 'invisible' air supply. Once everything is working properly, I think I'll see if I can aerate the water before it enters the pond, which might be a better solution.

There seems to be a wide divergence of opinion on pond heating. I decided (at this stage) not to implement it. To me, heating an outside pond containing 10 tons of water seems a very expensive thing to do. Advice is to heat it to 12 degrees Celsius through the winter, which keeps the fish active and feeding. Well, the temperature in the UK is usually less than that for 5 months a year. If your pond isn't insulated and covered (mine isn't) then heating it is going to be expensive. If you don't heat, I think that you do have to think about winter management.