Aquarium Water changes

[CbtJoe]

I have a few small koi from my pond in a quarantine aquarium tank. Giving them antibiotics to help with ulcers/fin rot. My question is about the daily water changes. Now that the pond is all situated and has other fish healthy and happy and the water is in perfect limits, can I use the pond water as my change water for the few koi in the aquarium or should I contribute to use tap water?