I've noticed in the last few days that a couple of my young ghost koi and one of my older koi have started rubbing themselves against the side of the pond, almost as thought they've got an itch if you know what i mean.
I've had a look at the older Koi (the younger ones are a pain in the neck to catch!). I can't see anything out of the ordinary on it. The only other thing i will add is that it doesn't seem to be eating like it did before, it used to be one of the first ones to the top to get the food, the last couple of days it doesn't seem that interested.
There's been a couple of times this morning that i saw it rub it's side against the bottom of the pond and then it suddenly shot up out of the water and back in again.
If there are no sign of any parasites or white spots then it could be down to the water parimetors do you test your pond water at all for Amonnia, Nitrite, nitrate etc if so what are your readings because if they are not right this can make the fish flash as if they have an itch. In your other post you mentioned you had a koi die for no apparent reason so this could be connected.
another thing i've noticed too, is that the older koi now just seems to be hovering around not doing anything, with it's mouth near the surface of the pond just constantly opening and closing. The only time it now swims around is when it shoots of to rub itself against the pond.
For test kits I prefer the ones by Aquarium pharmeceuticals. I find them easy to ready, if I havent got the name correct I will correct it after I have checked it. With others I have tried I found it very hard to say what colour I was looking at.