An Introduction to Bottom Drains of Koi Pond Construction , Monday, July 20, 2009 at 2:14 AM, in

In this article of koi pond construction we cover bottom drains, including how many your pond will need, where to locate them and what piping to use.
Bottom drains count for the vast majority of the water circulation in a Koi pond - by that I mean that the relative volume of water that they take up from the pond is massive when compared to that of say, your surface skimmer.
The vast majority of solids will sink to the bottom of the pond in time, where ideally, they will be sucked into the bottom drain and fed to the filter systems where they will be extracted from the pond water.
When designing your Koi pond construction, a rule of thumb is one bottom drain for the first 15,000 liters and then one drain for every 10,000 - 15,000 liters thereafter. Of course, the size of your pond will have a lot to do with this - as will the flow rate you want through your filter systems. If you turn your pond water over every two hours, and the size is 50,000 liters you will need 25,000 liters per hour coming from your bottom drains.


A gravity fed 110 mm bottom drainpipe will flow at approximately 10,000 l/hr. This means that our 50,000 liter pond with 2 bottom drains will turn the pond over once every two and a half hours. In terms of your Koi pond construction this is well within acceptable limits. Three bottom drains will turn the pond over every 1 hour 40 mins, so provided the filtration system can handle 30,000 l/hr, this is also an acceptable solution.
Bottom drains - or the pipe work from the drain to the settlement chamber should not be too long. This is because although there is water flow through the pipe work, the heavier solids tend to settle out and can build up in the pipe work itself.
Using thinner pipe may have a higher flow rate, but It is understood that using thinner pipe in your Koi pond construction will have a tendency to block much more easily. In addition, a 50 mm bottom drain pipe simply will not be able to give you enough flow, under gravity, to feed your filter system adequately unless you install a lot more of them. The additional expense could also make the price of building the pond increase dramatically.
The only way to make a 50 mm bottom drain work is to suck the water through via a pump. This is not a recommended design because the pump impeller will just churn the solids in the pond into mush - making it very much harder for the mechanical filter system to strip the solids out of the pond water. The compromise in Koi pond construction is simply not worth it - it is highly recommended to use 110 MM piping on your drains.



Accumulated build up in the pipe work is something that you simply don't want if you can avoid it. Solids accumulating anywhere in a Koi pond are bad news. This is why stand pipes are used - they help to purge the drainpipe work of accumulated solid debris and muck. It is also a good reason to have a settlement chamber.

Jessica Arons specializes in Koi fish care and is currently working with the Koi Fish School team. For more great tips on Koi pond construction visit The Koi Fish School today.