Koi pond requires certain specifications. One of the requirement is to have bottom drain. Unlike other kind of ponds, koi pond has to be design to accomodate the need for water quality. The shape of the pond's floor has to direct any debris and fish waste into the bottom drain. Another feature is to have a straight down wall with the minimum depth of 3 feet to prevent racoon and other predatory animal. Build it properly, you will have the pond that will last you a life time of enjoyment.