Koi Pond – Bottom Drains

Bottom drains

You should fit your bottom drains while the pond is under construction. This is BEFORE you pour the concrete into the base. After you’ve got your bottom drains in, get all the pipework for the bottom drains laid out in position as well, cut to shape, lay it then pour in the concrete.

In the few instances where it is not possible to connect the drainage into the main drains, you will need to use a soakaway (but only if you do not have nearby neighbours).

Use a discharge chamber if the main drain is above the height of the pond. You can then pump it to the drain with a pump that has a float level fitted.

The picture on left shows a typical PVC bottom drain that is used with a liner.

These are usually deep large sump 10 to 12 inches diameter and about 6 inches deep. They have 4 inch socket to take pressure pipe, which is then taken directly to the drain box where a 4 inch stand pipe with `O\’ ring is fitted.

You can also purchase bottom drains made of fibreglass, although these are not very popular now.

Once you’ve completed the pond, fit the mushroom cover over the unit. There is a gap between the cover and the top flange of about ½ inch. This will give a good purging effect when the stand pipe is pulled.

Fit the dome when there is about one foot of water in the pond so that there is no air trapped underneath. This will then cause the dome to be forced up when the pond is full, making it difficult to replace.

You can also drill two 7 mm holes in the top of the cover to ensure that there are no trapped air underneath.

Installing bottom drains

Depending on the size and shape of the pond, as well as your preference, you will need to decide the number of bottom drains required. If you have a pond that is rectangular with 12ft x 10ft measurements, then two bottom drains would suffice.

If you have a 18ft x 12ft pond then three bottom drains are usually used.

Connect each drain to its own pipe direct to the Vortex or filter system.

This connection should be as straight as possible with only one bend at right angles up to the stand pipe for a maximum flow rate.

To enhance flow of rate and maximize it, you should also use a 4″ long radius bend instead of a 4” pipe elbow.

If you’re using terrain pipe then the elbows are not as tight like the pipe elbow.

Pipe elbow Pipe bend

If you are using a Vortex, you will need to use more than one elbow to connect the pipes to the inlet, but make sure that the flow is as smooth as possible. Once you’ve laid out your pipes, you will then bury the network in concrete at the base of the pond, so make sure your design is right the first time.

Tip: Any vertical pipework outside the base of the pond should be covered with stone dust or sand and not concrete. This will then allow you to alter the pipe work later.