Why treat when you have nothing wrong? Medications are not good for fish or ponds, you should use them is little as is necessary, sorry for my negativity but in all my years keeping koi I've never done anything like this and never had a problem in spring. I live in the UK so maybe you guys do things differently?
As for feeding, I feed them as much as they will eat quickly, just as I do all year round. They will not eat it if it's not right, usually they eat, to some extent, right down to 5 or 6 degrees. Never had a problem.