Did I pull the plug a little early? Maybe, although the pond seemed to lose the dye quite easily, making me wonder if the build up of general waste gave the chemical too much work to do before getting at the parasites. Keeping the ranchu in an unfiltered pond made it very difficult to keep the water in great condition whilst medicated accurately. I'm confident the dosing levels were on the mark.
Next step? I'm contemplating two options. One, is a 10 minute bath treatment in dissolved salt at a high dosage (15 - 20 grams per litre). This is a method used by a widely recognised high quality Ranchu breeder. The alternative is treating the fish with a Permanganate treatment. I've read many posts from enthusiasts having successful results with Permanganate, although i'm equally aware of just how harsh the treatment can be on the fish.
The fish still appear happy and active enough, although somewhat disappointed to be out of the much larger pond!