Yes it can be fluke but in somewhat advanced stages, you would see lesions. It isn't anchor worm if you don't see the fine threads hanging off the koi. As far as fish lice, that's a guess. Being one fish, the platinum ogon is flashing and not the rest, it doesn't sound like an infestation. Fluke are almost always from poor water conditions.
I'm really trying to help and pin it down but without a microscope, it's difficult.
The symptoms of fluke parasites on koi fish are many. Look for fluke in koi fish that exhibit these signs:
Lethargy, redness or irritated skin, excessive mucus covering on skin, isolation and weakness. You will notice that your fish become thin to emaciated, become listless, and see the appearance of a milky film surrounding the fish. This is referred to as ‘gray slime disease’ and is the koi’s response to the aggressive feeding by heavy infestations of the parasite. Scraping or rubbing in an attempt to rid the pests are also symptoms of fluke parasite on koi fish. Bacterial infections may follow advancing to ulcers and scars.
If this is not the case, and it sounds like it isn't, fluke can be ruled out & definitely anchor worm is out.
The Cyropro would be treating nothing unless it were fish lice.
As for fish lice:
The adult Fish Lice parasite is flat and oval shaped with four pair of legs used for swimming. It looks like a glob of clear jelly infused with pepper. The eyes are recognizable on the face as two prominent black specks. It has suction type discs used to adhere to the host. Fish lice on koi are quite mobile; you can actually see them move along the fish’s skin. They can even swim from one fish to another if they so choose. A fish lice parasite can actually live for several weeks without attaching to a host fish! Adults may grow to ½ inch in size. The female leaves the host fish to lay her eggs onto plants and anything else in your pond. She releases up to 500 fertilized eggs at a time. These fish lice eggs will hatch in two to eight weeks, depending on water temperature.
Fish lice have tiny mouthparts that are stingers. These stingers are used to pierce the flesh and dine on the koi’s blood and mucus. The louses constant movement coupled with constant stinging cause your koi’s skin to become red and irritated. As the lice move around on the fish it leaves open holes in the koi’s slime coat which allow bacteria to infiltrate the skin and cause havoc, generally resulting in sores or ulcers.
So if you're experiencing non of the above symptoms as time passes, one koi flashing is a good thing as there doesn't appear to be any apparent breakout, at least not yet.
What are your thoughts?