I have not used copper sulfate in a koi pond as there are better/safer products out there. I have used pennies in aquaria to take care of parasites, but as soon as the fish show any signs of toxicity, then the pennies are removed and a good water change is administered to remove the toxic levels of copper. Reading Doc Johnson, he states the dosage of copper sulfate needed in ppm is equal to the Total Alkalinity (KH) divided by 100. It is very toxic at levels above this dosage. He goes on to state that Cupramine by SeaChem is a much safer copper treatment, effective against parasites at 0.2mg/L, but safe for fish up to 0.6 or 0.8mg/L
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard