There has been great debate about this over the years , there is a formula of one fish per 1,000 gallons US then 100 gallons per fish there after .
That said I would only own one koi if we followed this but everyone I've ever talked to about this finds this to be contradictory to say the very least .
I have a total of of 12 koi in our 1,000 gallon imperial pond , we get good grroth rate great colouration and most importantly they live in a stress free enviroment .
Ok so how do we come by this hypothasis?
DrCase has a good point by stressing them out by moving them they stopped eating became unhappy with their new surroundiings , though as soon as they were back in their ow pond the not only started eating but bred as well , I've often thought a change in the signature of the water chemistry as being a major stressor.....hard water to soft water and vica versa it makes for unhappy fish..
Every time I feed our koi I have them under constant observation , I have a number of koi I will watch intensely namely a Kohuku and white ogon [not pirichina].
Fish with ite skin are your best first line of defence in that when under any stress whatsoever they will pink up in both body and fins , at no time do I observe pinking , yes after the lightening strike the kohaku pinked up it was one of three koi that took the brunt .
However the Ogon did not exhibit any stress response to this.
As to water quality we test ous on a weekly basis , I see nothing wrong in this perhaps its a throwback from indoors I dont know but others on this site also do this.
Waterchanges ae a regular feature again most probably a throwback but looking at waterchanges the water I put back into the system goes through a water filter which removes Chlorine befor it even goes into the pond and as such is not as hit and miss as using dechlorination liquid .
I do not mention chloramines simply because that idea was shelved here in the UK, one of Spikes mantras is if in doubt water change in our view good sound advice
Nutriional wise we follow the correct feeds as per the seasons and quit at 10c [the koi having take on the fat they need during late spring summer when we switch to a high Protien food called NTLabs Medikoi Probiotic , many fish keepers use cheaper foods that aren't really suitable for what you need to do in pellet cotent crude protion ash etc .
The amount of surfaces we have for helpful bacteria is simply phenominal including Jap matting K1 Bio balls bio chips etc.
All but the first filter support a miriad of smaller creatures some that filter water , blood worm etc this indicates a good and working biological/mechanical filter.
Fow rates are an important thing , our pipe width being 4" we get a good flow rate per hour , many fish keepers do not take this into concideration .
Our pond being a former QT fasility holdng pond supported many more koi than they do today upwards by a long chalk than what we have in the pond today.
But thats just our pond point taken though nothing wrong with helpful pointers .
However many people do not do their homework first they build a pond and stock it to th gills so to speak often with inadiquate filtration then wonder why their fish die.
They need education as such it is our job to educate them in as gentle a way as we possibly can only that way do we get our message across its amazing when someone starts along the route of Fish health it seems to invigerate them , they find that there are worlds within worlds Parasite Bacteria Virus's Pathogens .
The microscope is often the clincher for them . Ive seen it with ny own eyes , I'm currently teaching a friend [Vals first kiss at school lol] he enlisted in the Army went to Iraq saw and did terrible things such as killing people , he came away with PTSD .
Koi are helping in his recovery a positive thing , [it worked for me also].
I will add the points raised to the article when any other points you raise come through then if you wish add your name to my work as a sort of joint enterprise if you wish. ?
Dave