689.9 gallons would be the volume of water.
This is know where near enough for you to succesfully keep koi.
As for using the Bakki shower i would first redesign your pond to give a minimum of 1,500 to 2,000 gallons to have any chance of keeping koi in a healthy enviroment.
I am assuming it will be your first time keeping koi and like to say welcome to the world of koi however as all of the members on this forum and many other forums we have to start with learning the basics
First of many things to learn is that Koi excrete far far more ammonia than your basic pond goldfish hence the need for good quality water and it is water we keep and not the koi .
If your water is kept in the best condition the Koi will flourish, you will see many members on here talking about ammonia,nitrite and nitrite to name a few then you have the RO debate the list is endless to the point we are always looking to better the quality of our water we keep the koi in.
Please dont feel put off by all this as it does sound like a mine field to begin with however there is some very knowledgeable members on this forum who are more than willing to help with advice and even building your pond.
Hope this hasnt put you off and please feel free to ask and ask more because thats how we all learned
As a guide a 10ft x 5ft x 4ft would give you 1,246 gallons but 6ft wide would be 5 gallon short of 1,500
Rick
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