Oxygen – Oxygen to koi is very important. Koi can live in a pond with a low oxygen level but they will never thrive. Low oxygen affects their metabolism and in turn their appetite. You will never be able to grow a koi to it’s full potential without plenty of oxygen in the pond at all times. How the pond is going to provide this oxygen needs to be designed into the pond from the start. A waterfall is a good start. Jets can be a real source for oxygen. Adding a built in air diffuser on the bottom of the pond that is run by an air pump can also add a great amount of oxygen. What is nice about this addition is that if the pump ever fails causing the waterfall and jets to stop, you still have a serious source of oxygen still being provided to the pond. Even if you choose not to run it all the time, it can easily be turned on in an emergency. See Sacramento koi bottom drain cover with air diffuser.