How to Build a Koi Pond - Water Returns and Venturis...

You have to return the water to the Koi pond from the filter system somehow. Use this to you and your pond's advantage...

Building a Koi pond - Filter water returns and venturis explained

Once the water has passed through your filter system, it will need someway of getting back into the pond. In South Africa, this has traditionally been done by plumbing pipework into the side of the pond, and then aiming the 'jet' of the pipe to circulate the water around the pond.

Whilst this is not in itself a bad thing, it can be improved on.

A pipe emanating from the side of a pond wall merely adds one more thing for a Koi to injure itself on. During a feeding frenzy, or a spawning frenzy, it is quite possible for a Koi, naturally the most valuable one in your pond, to damage itself on the pipe work.

A much neater solution is to lay the return pipe at an angle to the wall, in the direction that you want the water to flow. The, simply cut the pip off flush with the wall. The water will follow the direction of flow (according to the angle of how you have laid the pipe).

Of course, if you want to add a venturi to such a system you will need to cater for this when building the pond's side wall.

What is a venturi?

Without getting technical, a venturi is simply a small thin pipe that is open the the atmosphere on one end and attached into the end of the water return on the other, a short distance from the edge of the pipe exit. As the water flows through the pipe it sucks air down this tube and this air then gets mixed with the water flow and ends up in the pond normally in a fine mist of bubbles. It is a great way to get oxygen into your pond using nothing other than the flow rate of water in the pond return pipe.

The faster the flow rate, the more air is sucked in.

The downside to a venturi is that unless properly located, they can obscure the water surface substantially, making viewing your Koi challenging. They can also be quite noisy but a great tip for that is to take a large chunk of low density foam and stick it over the end of the tube - that shuts the venturi up as well as preventing any bugs from getting in and jamming the pipework.

A far better idea is to use a dedicated air pump in a Koi pond in order to introduce air. This has two primary advantages.

1. If your main pump fails for whatever reason, the Koi pond will still be oxygenated by the air pump which is critical. I cannot stress enough how often I have seen Koi ponds lose all their big Koi because of a pump failure and lack of oxygen as a direct result.

and

2. You can locate this air to be dispensed anywhere you choose. A simple air bar (or even a ring of perforated tube) incorporated into the design of the pond will ensure that it need not be seen and that air pumped into the pond can then be positioned such that your view of the Koi is not disturbed.

You can never have too much air in a Koi pond! But do not induce air into the system under pressure, such as occasionally happens when a pump sucks air - this is not a good idea. The pump compresses the air into the water, raising the dissolved soluble maximum by a small percentage (it is called super saturated water). This super saturated water, if breathed in by a Koi, releases tiny gas bubbles inside the body of the Koi.

These tiny bubbles end up blocking fine capillaries in the fins, and this leads to fin rot, bacterial infections and a lot of unpleasantness in the Koi pond.

More on water returns

It is normally a good idea to use the water returns to try and gently circulate the whole pond water mass in the same direction. In an ideal 'half water melon' pond, pick a direction and aim your water returns so that the same water mass rotation is amplified.

You do not want to locate your water returns either too deep or to shallow. Normally about 300 - 600mm below the surface is good. You can have a 'deep water' return or two but make sure that these don't aim directly at the bottom drains - else all that happens is that the water from the filters ends up being filtered again almost immediately whilst the rest of the pond just stands idle.

Use your returns to try and prevent any dead spots in the pond, i.e. spots where the water remains stagnant and doesn't circulate. Remember that you want the water to be turned over through the filter system as evenly as possible and whilst this might not be possible to achieve you should strive to get as close to this ideal as possible.

Koi pond water returns can be used effectively to help clean out tricky areas where you might otherwise develop a build up of solids and/or debris.

Deep water returns can also be effective 'Koi exercisers'. Koi love to swim against currents and it's good for their health and body shape. Just be careful not to overdo it - in winter when they are in 'go slow' mode you don't want to constantly irritate them with a gulf stream of water pushing them all the time.

Use your common sense with water returns - it and they will serve you well.