I am not trying to offend anyone. There is nothing wrong with any of the these. It just that here, the purpose of a pond is to provide a healthy home for Koi. Koi can live in the others, but not in the numbers that necessitate a Koi pond. Neither of the above is dependent on the other.
Water is an excellent solvent.
It is possible to have unhealthy, toxic, crystal-clear water. One of the reasons swimming pool filter systems do not work very well on Koi ponds is that they are designed for mechanical and chemical filtration of water. Swimming pool filter systems rely on a pump that is operated for a set time each day. Pumps used for biological filters are required to run 24 hours a day. Commercially Available Bio-filters.