I am currently babysitting a friend's koi all still very small between 12 and 20 cm. They have been with me for about a month now and all is going well all the water parameters are kept in check on a weekly basis, Last night I went out to the ponds and noticed that there is what looked to me at first like a unfirmiliar fish umong those I have come to know, a plain jane white fish,after closer inspection I saw very faint Hi markings that looked alot like a Kohaku that was there and was now no where to be seen. So it would seem like this Kohaku lost all his Hi overnight. Is this normal ? because all the other Kohaku,Sanke and showa still have theire Hi and theirs don't look like their fading at all it seems to just be the one that went from a Kohaku to a white fish.

Hi Bubbles.

Kohaku's have a greater tendency to loose colour(Hi) than the Sankes and Showa's. Probably your PH is different to what the fish are used to and a different type of sun exposure, different food and new stress(moving them to your place) often causes that the Hi fades. Genetically it is normally not a good fish if it loses colour that fast. Introduce more vitamins (lettuce) to combat this.

I have not experienced such a fast colour loss, but over a few days yes.

Thanks I will get some lettuce. do I tie it to a string to suspend it or just let it float and let them have at it ?

Just brake it into small pieces. Initially they are not keen, but gradually they snap them up before it reaches the skimmer.