It is inevetable that, sooner or later, you will need to treat your Koi, even if it is only to give them a prophylactic anti-parasite tretment before the onset of Winter.
It is critical to the health of your Koi that you measure precisely any treatments you put in your pond.
What's the worst that can happen ?
Well, the worst that can happen is that it is easily possible to overdose to the point where you may kill your Koi.
Take great care when calculating the volume of your pond, follow the dosages given with the treatment, measure it out accurately and all will be well.