Bottom Drain Science and Popularity on the Rise

Posted by Blue Thumb on Apr 21st 2021

Bottom Drain Science and Popularity on the Rise

Despite popular belief, bottom drains are not just for pools. The growing popularity within the pond industry is leading to new standards for koi ponds and water garden pond installation. The pond maintenance requirements are drastically reduced along with koi health benefits being improved. Bottom drains are not only efficient but can add aeration, so the yearly spring pond clean-out practices are less needed. Most contractors are accustomed to this springtime practice and dedicate a lot of money and effort with little time for spring start-up projects. The ability to up-sell on a gravity flow bottom drain along with a pre-filter and an external pump allows landscape contractors to improve profit margins with add-on sales.


Gravity Flow Bottom Drains are only truly effective with proper aeration and proper water flow rate plumbing. Choosing the right size bottom drain for your koi pond project is very important otherwise it will become useless. As a rule, follow these simple guidelines:

An 8′ diameter pond requires a 3″ Gravity Flow Bottom Drain

A 10′ diameter pond requires a 4″ Gravity Flow Bottom Drain

Bottom drains are not only efficient but can add aeration and the yearly spring clean-out practices are no longer needed.

Please keep in mind this is a general rule and call your local pond distributor for recommended size and quantity of drains. Gravity Flow drains are recommended to allow for pond water to carry the fish waste and other material to the pre-filter. Adversely, with suction-driven bottom drains the water flow rate is increased so much so that fish waste and other material can be broken down not allowing the filter to accomplish proper pond filtration. Bottom drains along with biological, mechanical, and sterilization filtration can make any koi pond beautiful and clean.


Many bottom drains can be plumbed directly to the skimmer as well. A valve must be placed on the inside of the skimmer to control the flow rate. However, it is recommended to attach these to a pre-filter to allow for proper filtration and to maximize bottom drain efficiency. One of the most important things to remember when installing a bottom drain is that it is best to partner with pond aeration as well as a sloped bottom (bowl-shaped) to force pond muck to the drain. In closing, pond bottom drains can be a great tool if partnered with the correct pond aeration kit, pond design, and pond filtration.

Do you have a project that bottom drains might be suitable for? Send us an email with your project info and we’ll get started specifying the necessary equipment.